diff --git a/src/zen/common/styles/zen-buttons.css b/src/zen/common/styles/zen-buttons.css
index d94c2c367..a3dfd404a 100644
--- a/src/zen/common/styles/zen-buttons.css
+++ b/src/zen/common/styles/zen-buttons.css
@@ -38,6 +38,10 @@ dialog[defaultButton="accept"]::part(dialog-button) {
       padding-inline-end: 4em;
     }
 
+    @media (-moz-platform: linux) {
+      padding-inline-end: 3.1em;
+    }
+
     &::after {
       border-radius: 4px;
       font-weight: 600;
diff --git a/src/zen/tests/manifest.toml b/src/zen/tests/manifest.toml
index 60c0975dc..18334b2f8 100644
--- a/src/zen/tests/manifest.toml
+++ b/src/zen/tests/manifest.toml
@@ -25,5 +25,9 @@ disable = [
   "browser_setDesktopBackgroundPreview.js",
 ]
 
+[tabMediaIndicator]
+source = "browser/components/tabbrowser/test/browser/tabMediaIndicator"
+is_direct_path = true
+
 [tooltiptext]
 source = "toolkit/components/tooltiptext"
diff --git a/src/zen/tests/media/browser.toml b/src/zen/tests/media/browser.toml
new file mode 100644
index 000000000..52752f239
--- /dev/null
+++ b/src/zen/tests/media/browser.toml
@@ -0,0 +1,16 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+[DEFAULT]
+support-files = [
+  "head.js",
+]
+
+["browser_media_metadata.js"]
+
+["browser_media_mute.js"]
+
+["browser_media_next_track.js"]
+
+["browser_media_shows_on_tab_switch.js"]
diff --git a/src/zen/tests/media/browser_media_metadata.js b/src/zen/tests/media/browser_media_metadata.js
new file mode 100644
index 000000000..a048b8cac
--- /dev/null
+++ b/src/zen/tests/media/browser_media_metadata.js
@@ -0,0 +1,63 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// User flow:
+//   1. A page (think Spotify, YouTube Music) plays media and publishes
+//      title/artist via navigator.mediaSession.metadata.
+//   2. User switches off that tab, media bar appears.
+//   3. The title and artist labels in the bar show what the page published.
+//   4. The page then updates the metadata mid-playback (next song starts).
+//   5. The bar updates live, without the user having to switch tabs again.
+//
+// This is what makes the bar feel connected to the playing page instead of
+// a generic "something is playing" indicator.
+
+add_task(async function test_media_bar_shows_metadata_from_page() {
+  const originalTab = gBrowser.selectedTab;
+  const mediaTab = await addMediaTab();
+  await BrowserTestUtils.switchTab(gBrowser, mediaTab);
+
+  try {
+    await setMediaSessionMetadata(mediaTab, {
+      title: "Sandstorm",
+      artist: "Darude",
+    });
+    await playVideoIn(mediaTab);
+    await BrowserTestUtils.switchTab(gBrowser, originalTab);
+    await waitForMediaBarVisible();
+
+    const titleEl = document.getElementById("zen-media-title");
+    const artistEl = document.getElementById("zen-media-artist");
+
+    await BrowserTestUtils.waitForCondition(
+      () => titleEl.textContent === "Sandstorm",
+      "title label reflects the page's mediaSession metadata"
+    );
+    Assert.equal(
+      artistEl.textContent,
+      "Darude",
+      "artist label reflects the page's mediaSession metadata"
+    );
+
+    // Page updates metadata mid-playback.
+    await setMediaSessionMetadata(mediaTab, {
+      title: "Levels",
+      artist: "Avicii",
+    });
+    await BrowserTestUtils.waitForCondition(
+      () => titleEl.textContent === "Levels",
+      "title updates live when the page changes its mediaSession metadata"
+    );
+    Assert.equal(
+      artistEl.textContent,
+      "Avicii",
+      "artist updates live alongside the title"
+    );
+  } finally {
+    await pauseVideoIn(mediaTab);
+    BrowserTestUtils.removeTab(mediaTab);
+    gBrowser.selectedTab = originalTab;
+  }
+});
diff --git a/src/zen/tests/media/browser_media_mute.js b/src/zen/tests/media/browser_media_mute.js
new file mode 100644
index 000000000..766059fd0
--- /dev/null
+++ b/src/zen/tests/media/browser_media_mute.js
@@ -0,0 +1,64 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// User flow:
+//   1. User plays a video, switches tabs, media bar appears.
+//   2. User clicks the mute button on the Zen media bar.
+//   3. The underlying tab actually goes silent (browser.audioMuted flips).
+//   4. The media bar reflects that with the `muted` attribute so the icon
+//      changes.
+//   5. Clicking again unmutes.
+//
+// If this breaks, the user sees a mute button that looks toggled but the
+// audio keeps playing — or worse, the tab is muted but the button still
+// says "unmuted".
+
+add_task(async function test_mute_from_media_bar() {
+  const originalTab = gBrowser.selectedTab;
+  const mediaTab = await addMediaTab();
+  await BrowserTestUtils.switchTab(gBrowser, mediaTab);
+
+  try {
+    await playVideoIn(mediaTab);
+    await BrowserTestUtils.switchTab(gBrowser, originalTab);
+    await waitForMediaBarVisible();
+
+    ok(
+      !mediaTab.linkedBrowser.audioMuted,
+      "precondition: playing tab starts unmuted"
+    );
+    ok(
+      !mediaBar().hasAttribute("muted"),
+      "precondition: media bar has no muted attribute"
+    );
+
+    clickMediaButton("zen-media-mute-button");
+    await BrowserTestUtils.waitForCondition(
+      () => mediaTab.linkedBrowser.audioMuted,
+      "tab becomes muted after clicking the media bar mute button"
+    );
+    ok(
+      mediaBar().hasAttribute("muted"),
+      "media bar reflects the muted state in its attribute"
+    );
+
+    clickMediaButton("zen-media-mute-button");
+    await BrowserTestUtils.waitForCondition(
+      () => !mediaTab.linkedBrowser.audioMuted,
+      "clicking again unmutes the tab"
+    );
+    ok(
+      !mediaBar().hasAttribute("muted"),
+      "media bar drops the muted attribute"
+    );
+  } finally {
+    if (mediaTab.linkedBrowser.audioMuted) {
+      mediaTab.toggleMuteAudio();
+    }
+    await pauseVideoIn(mediaTab);
+    BrowserTestUtils.removeTab(mediaTab);
+    gBrowser.selectedTab = originalTab;
+  }
+});
diff --git a/src/zen/tests/media/browser_media_next_track.js b/src/zen/tests/media/browser_media_next_track.js
new file mode 100644
index 000000000..f4797e7e0
--- /dev/null
+++ b/src/zen/tests/media/browser_media_next_track.js
@@ -0,0 +1,74 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// User flow:
+//   1. A music page registers a "nexttrack" action handler (like most
+//      streaming sites do).
+//   2. User is on another tab, media bar is showing with the next-track
+//      button enabled.
+//   3. User clicks next-track.
+//   4. The action fires inside the page — the page is responsible for
+//      loading the next song. Zen's job here is to relay the click.
+//
+// Also guards the button-enablement logic: if the page does NOT register a
+// handler, the next-track button must be disabled. Otherwise clicks go
+// nowhere and users think the bar is broken.
+
+add_task(async function test_next_track_relays_to_page() {
+  const originalTab = gBrowser.selectedTab;
+  const mediaTab = await addMediaTab();
+  await BrowserTestUtils.switchTab(gBrowser, mediaTab);
+
+  try {
+    await playVideoIn(mediaTab);
+    await setMediaSessionActionHandler(mediaTab, "nexttrack");
+
+    await BrowserTestUtils.switchTab(gBrowser, originalTab);
+    await waitForMediaBarVisible();
+
+    const nextButton = document.getElementById("zen-media-nexttrack-button");
+
+    // supportedkeyschange propagates asynchronously; wait for the bar's
+    // next-track button to become enabled before clicking.
+    await BrowserTestUtils.waitForCondition(
+      () => !nextButton.disabled,
+      "next-track button becomes enabled once the page registers a handler"
+    );
+
+    const actionFired = waitForMediaSessionAction(mediaTab);
+    clickMediaButton("zen-media-nexttrack-button");
+
+    const result = await actionFired;
+    ok(result, "page's nexttrack MediaSession handler was invoked");
+  } finally {
+    await pauseVideoIn(mediaTab);
+    BrowserTestUtils.removeTab(mediaTab);
+    gBrowser.selectedTab = originalTab;
+  }
+});
+
+add_task(async function test_next_track_button_disabled_without_handler() {
+  const originalTab = gBrowser.selectedTab;
+  const mediaTab = await addMediaTab();
+  await BrowserTestUtils.switchTab(gBrowser, mediaTab);
+
+  try {
+    // Deliberately do NOT install a nexttrack handler.
+    await playVideoIn(mediaTab);
+    await BrowserTestUtils.switchTab(gBrowser, originalTab);
+    await waitForMediaBarVisible();
+
+    const nextButton = document.getElementById("zen-media-nexttrack-button");
+    Assert.equal(
+      nextButton.disabled,
+      true,
+      "next-track button stays disabled when the page registers no handler"
+    );
+  } finally {
+    await pauseVideoIn(mediaTab);
+    BrowserTestUtils.removeTab(mediaTab);
+    gBrowser.selectedTab = originalTab;
+  }
+});
diff --git a/src/zen/tests/media/browser_media_shows_on_tab_switch.js b/src/zen/tests/media/browser_media_shows_on_tab_switch.js
new file mode 100644
index 000000000..783a88af1
--- /dev/null
+++ b/src/zen/tests/media/browser_media_shows_on_tab_switch.js
@@ -0,0 +1,74 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// User flow:
+//   1. User opens a page with audio and hits play.
+//   2. User switches to a different tab.
+//   3. The Zen media control bar should appear (so the user can still
+//      pause/skip without going back to the noisy tab).
+//   4. User switches back to the audio tab.
+//   5. The media bar should hide again — it's redundant next to the real
+//      page controls.
+//
+// This covers the real contract users see: the DOMAudioPlaybackStarted →
+// TabSelect → showMediaControls chain in nsZenMediaController, plus the
+// inverse path on selecting the playing tab. A regression anywhere in that
+// chain (event wiring, the 500ms tab-switch debounce, the hidden attribute
+// flip) surfaces as a bar that either never shows or never hides.
+
+// note: We keep setting timeouts because media player takes a bit to
+// get removed (after the animation, more specifically)
+
+add_task(async function test_media_bar_shows_when_switching_off_playing_tab() {
+  gZenMediaController.onControllerClose();
+  await BrowserTestUtils.waitForCondition(
+    () => !isMediaBarVisible(),
+    "media bar hides again once the playing tab regains focus"
+  );
+
+  const originalTab = gBrowser.selectedTab;
+  const mediaTab = await addMediaTab();
+  await BrowserTestUtils.switchTab(gBrowser, mediaTab);
+
+  ok(
+    !isMediaBarVisible(),
+    "media bar is hidden while the playing tab is the active tab"
+  );
+
+  try {
+    await playVideoIn(mediaTab);
+
+    ok(
+      !isMediaBarVisible(),
+      "media bar remains hidden while focused on the playing tab"
+    );
+
+    // Switch away. The controller schedules showMediaControls() on a 500ms
+    // timer; wait for the visibility flip rather than racing it.
+    await BrowserTestUtils.switchTab(gBrowser, originalTab);
+    await new Promise(r => setTimeout(r, 1000));
+    await BrowserTestUtils.waitForCondition(
+      isMediaBarVisible,
+      "media bar becomes visible after switching off the playing tab"
+    );
+
+    Assert.equal(
+      gZenMediaController._currentBrowser?.browserId,
+      mediaTab.linkedBrowser.browserId,
+      "media controller is bound to the media tab's browser, not the selected tab"
+    );
+
+    await BrowserTestUtils.switchTab(gBrowser, mediaTab);
+    await new Promise(r => setTimeout(r, 1000));
+    await BrowserTestUtils.waitForCondition(
+      () => !isMediaBarVisible(),
+      "media bar hides again once the playing tab regains focus"
+    );
+  } finally {
+    await pauseVideoIn(mediaTab);
+    BrowserTestUtils.removeTab(mediaTab);
+    gBrowser.selectedTab = originalTab;
+  }
+});
diff --git a/src/zen/tests/media/head.js b/src/zen/tests/media/head.js
new file mode 100644
index 000000000..82de52c6c
--- /dev/null
+++ b/src/zen/tests/media/head.js
@@ -0,0 +1,96 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Shared mozilla-central fixture from the Picture-in-Picture tests: an HTML
+// page with two looping <video src="gizmo.mp4"> elements (with and without
+// controls). Looping keeps playback stable across slow CI, and using a real
+// <video> element is closer to what Zen users actually play (YouTube, etc.)
+// than a bare <audio>.
+const MEDIA_PAGE =
+  "https://example.com/browser/toolkit/components/pictureinpicture/tests/test-page-with-sound.html";
+const VIDEO_SELECTOR = "#with-controls";
+
+async function addMediaTab() {
+  const tab = BrowserTestUtils.addTab(gBrowser, MEDIA_PAGE, {
+    skipAnimation: true,
+  });
+  await BrowserTestUtils.browserLoaded(gBrowser.getBrowserForTab(tab));
+  return tab;
+}
+
+async function playVideoIn(tab) {
+  await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [VIDEO_SELECTOR],
+    async selector => {
+      const video = content.document.querySelector(selector);
+      await video.play();
+    }
+  );
+  // Wait for the browser to actually consider the tab "playing" — this is
+  // what drives DOMAudioPlaybackStarted into the media controller.
+  await BrowserTestUtils.waitForCondition(
+    () => tab.soundPlaying,
+    "tab reports soundplaying"
+  );
+}
+
+async function pauseVideoIn(tab) {
+  await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [VIDEO_SELECTOR],
+    async selector => {
+      const video = content.document.querySelector(selector);
+      video.pause();
+    }
+  );
+}
+
+function mediaBar() {
+  return document.getElementById("zen-media-controls-toolbar");
+}
+
+function isMediaBarVisible() {
+  return !mediaBar().hasAttribute("hidden");
+}
+
+async function waitForMediaBarVisible() {
+  await BrowserTestUtils.waitForCondition(
+    isMediaBarVisible,
+    "media bar becomes visible"
+  );
+}
+
+// Click a toolbarbutton on the media bar. We dispatch a "command" event
+// directly because that's what the controller listens for and it sidesteps
+// the flakiness of synthesizing a mouse click on a small toolbar button.
+function clickMediaButton(id) {
+  const button = document.getElementById(id);
+  ok(button, `media bar button ${id} exists`);
+  button.dispatchEvent(new Event("command", { bubbles: true }));
+}
+
+async function setMediaSessionMetadata(tab, metadata) {
+  await SpecialPowers.spawn(tab.linkedBrowser, [metadata], async meta => {
+    content.navigator.mediaSession.metadata = new content.MediaMetadata(meta);
+  });
+}
+
+async function setMediaSessionActionHandler(tab, action) {
+  // Installs a MediaSession action handler and returns a promise that
+  // resolves when the handler fires. The promise is surfaced via a
+  // content-side global the caller can await.
+  await SpecialPowers.spawn(tab.linkedBrowser, [action], async a => {
+    content.wrappedJSObject.__zenActionFired = new content.Promise(resolve => {
+      content.navigator.mediaSession.setActionHandler(a, () => resolve(true));
+    });
+  });
+}
+
+async function waitForMediaSessionAction(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    return content.wrappedJSObject.__zenActionFired;
+  });
+}
diff --git a/src/zen/tests/mochitests/moz.build b/src/zen/tests/mochitests/moz.build
index 2acf5ec61..e6636a897 100644
--- a/src/zen/tests/mochitests/moz.build
+++ b/src/zen/tests/mochitests/moz.build
@@ -11,6 +11,7 @@ BROWSER_CHROME_MANIFESTS += [
 	"safebrowsing/browser.toml",
 	"sandbox/browser.toml",
 	"shell/browser.toml",
+	"tabMediaIndicator/browser.toml",
 	"tooltiptext/browser.toml",
 ]
 XPCSHELL_TESTS_MANIFESTS += [
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/almostSilentAudioTrack.webm b/src/zen/tests/mochitests/tabMediaIndicator/almostSilentAudioTrack.webm
new file mode 100644
index 000000000..0b8f8f746
Binary files /dev/null and b/src/zen/tests/mochitests/tabMediaIndicator/almostSilentAudioTrack.webm differ
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/audio.ogg b/src/zen/tests/mochitests/tabMediaIndicator/audio.ogg
new file mode 100644
index 000000000..bed764fbf
Binary files /dev/null and b/src/zen/tests/mochitests/tabMediaIndicator/audio.ogg differ
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/audioEndedDuringPlaying.webm b/src/zen/tests/mochitests/tabMediaIndicator/audioEndedDuringPlaying.webm
new file mode 100644
index 000000000..4f82b5da7
Binary files /dev/null and b/src/zen/tests/mochitests/tabMediaIndicator/audioEndedDuringPlaying.webm differ
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser.toml b/src/zen/tests/mochitests/tabMediaIndicator/browser.toml
new file mode 100644
index 000000000..9eac10b02
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser.toml
@@ -0,0 +1,44 @@
+[DEFAULT]
+subsuite = "media-bc"
+tags = "audiochannel"
+support-files = [
+  "almostSilentAudioTrack.webm",
+  "audio.ogg",
+  "audioEndedDuringPlaying.webm",
+  "file_almostSilentAudioTrack.html",
+  "file_autoplay_media.html",
+  "file_empty.html",
+  "file_mediaPlayback.html",
+  "file_mediaPlayback2.html",
+  "file_mediaPlaybackFrame.html",
+  "file_mediaPlaybackFrame2.html",
+  "file_silentAudioTrack.html",
+  "file_webAudio.html",
+  "gizmo.mp4",
+  "head.js",
+  "noaudio.webm",
+  "silentAudioTrack.webm",
+]
+
+["browser_destroy_iframe.js"]
+https_first_disabled = true
+
+["browser_mediaPlayback.js"]
+
+["browser_mediaPlayback_mute.js"]
+
+["browser_mediaplayback_audibility_change.js"]
+
+["browser_mute.js"]
+
+["browser_mute2.js"]
+
+["browser_mute_webAudio.js"]
+
+["browser_sound_indicator_silent_video.js"]
+
+["browser_webAudio_hideSoundPlayingIcon.js"]
+
+["browser_webAudio_silentData.js"]
+
+["browser_webaudio_audibility_change.js"]
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_destroy_iframe.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_destroy_iframe.js
new file mode 100644
index 000000000..f977d1d66
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_destroy_iframe.js
@@ -0,0 +1,50 @@
+const EMPTY_PAGE_URL = GetTestWebBasedURL("file_empty.html");
+const AUTPLAY_PAGE_URL = GetTestWebBasedURL("file_autoplay_media.html");
+const CORS_AUTPLAY_PAGE_URL = GetTestWebBasedURL(
+  "file_autoplay_media.html",
+  true
+);
+
+/**
+ * When an iframe that has audible media gets destroyed, if there is no other
+ * audible playing media existing in the page, then the sound indicator should
+ * disappear.
+ */
+add_task(async function testDestroyAudibleIframe() {
+  const iframesURL = [AUTPLAY_PAGE_URL, CORS_AUTPLAY_PAGE_URL];
+  for (let iframeURL of iframesURL) {
+    info(`open a tab, create an iframe and load an autoplay media page inside`);
+    const tab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      EMPTY_PAGE_URL
+    );
+    await createIframeAndLoadURL(tab, iframeURL);
+
+    info(`sound indicator should appear because of audible playing media`);
+    await waitForTabSoundIndicatorAppears(tab);
+
+    info(`sound indicator should disappear after destroying iframe`);
+    await removeIframe(tab);
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info("remove tab");
+    BrowserTestUtils.removeTab(tab);
+  }
+});
+
+function createIframeAndLoadURL(tab, url) {
+  // eslint-disable-next-line no-shadow
+  return SpecialPowers.spawn(tab.linkedBrowser, [url], async url => {
+    const iframe = content.document.createElement("iframe");
+    content.document.body.appendChild(iframe);
+    iframe.src = url;
+    info(`load ${url} for iframe`);
+    await new Promise(r => (iframe.onload = r));
+  });
+}
+
+function removeIframe(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+    content.document.getElementsByTagName("iframe")[0].remove();
+  });
+}
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaPlayback.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaPlayback.js
new file mode 100644
index 000000000..89143bf83
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaPlayback.js
@@ -0,0 +1,42 @@
+const PAGE = GetTestWebBasedURL("file_mediaPlayback.html");
+const FRAME = GetTestWebBasedURL("file_mediaPlaybackFrame.html");
+
+function wait_for_event(browser, event) {
+  return BrowserTestUtils.waitForEvent(browser, event, false, e => {
+    is(
+      e.originalTarget,
+      browser,
+      "Event must be dispatched to correct browser."
+    );
+    ok(!e.cancelable, "The event should not be cancelable");
+    return true;
+  });
+}
+
+async function test_on_browser(url, browser) {
+  info(`run test for ${url}`);
+  const startPromise = wait_for_event(browser, "DOMAudioPlaybackStarted");
+  BrowserTestUtils.startLoadingURIString(browser, url);
+  await startPromise;
+  await wait_for_event(browser, "DOMAudioPlaybackStopped");
+}
+
+add_task(async function test_page() {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:blank",
+    },
+    test_on_browser.bind(undefined, PAGE)
+  );
+});
+
+add_task(async function test_frame() {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:blank",
+    },
+    test_on_browser.bind(undefined, FRAME)
+  );
+});
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaPlayback_mute.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaPlayback_mute.js
new file mode 100644
index 000000000..fb771c23a
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaPlayback_mute.js
@@ -0,0 +1,118 @@
+const PAGE = GetTestWebBasedURL("file_mediaPlayback2.html");
+const FRAME = GetTestWebBasedURL("file_mediaPlaybackFrame2.html");
+
+function wait_for_event(browser, event) {
+  return BrowserTestUtils.waitForEvent(browser, event, false, e => {
+    is(
+      e.originalTarget,
+      browser,
+      "Event must be dispatched to correct browser."
+    );
+    return true;
+  });
+}
+
+function test_audio_in_browser() {
+  function get_audio_element() {
+    var doc = content.document;
+    var list = doc.getElementsByTagName("audio");
+    if (list.length == 1) {
+      return list[0];
+    }
+
+    // iframe?
+    list = doc.getElementsByTagName("iframe");
+
+    var iframe = list[0];
+    list = iframe.contentDocument.getElementsByTagName("audio");
+    return list[0];
+  }
+
+  var audio = get_audio_element();
+  return {
+    computedVolume: audio.computedVolume,
+    computedMuted: audio.computedMuted,
+  };
+}
+
+async function test_on_browser(url, browser) {
+  BrowserTestUtils.startLoadingURIString(browser, url);
+  await wait_for_event(browser, "DOMAudioPlaybackStarted");
+
+  var result = await SpecialPowers.spawn(browser, [], test_audio_in_browser);
+  is(result.computedVolume, 1, "Audio volume is 1");
+  is(result.computedMuted, false, "Audio is not muted");
+
+  ok(!browser.audioMuted, "Audio should not be muted by default");
+  browser.mute();
+  ok(browser.audioMuted, "Audio should be muted now");
+
+  await wait_for_event(browser, "DOMAudioPlaybackStopped");
+
+  result = await SpecialPowers.spawn(browser, [], test_audio_in_browser);
+  is(result.computedVolume, 0, "Audio volume is 0 when muted");
+  is(result.computedMuted, true, "Audio is muted");
+}
+
+async function test_visibility(url, browser) {
+  BrowserTestUtils.startLoadingURIString(browser, url);
+  await wait_for_event(browser, "DOMAudioPlaybackStarted");
+
+  var result = await SpecialPowers.spawn(browser, [], test_audio_in_browser);
+  is(result.computedVolume, 1, "Audio volume is 1");
+  is(result.computedMuted, false, "Audio is not muted");
+
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:blank",
+    },
+    function () {}
+  );
+
+  ok(!browser.audioMuted, "Audio should not be muted by default");
+  browser.mute();
+  ok(browser.audioMuted, "Audio should be muted now");
+
+  await wait_for_event(browser, "DOMAudioPlaybackStopped");
+
+  result = await SpecialPowers.spawn(browser, [], test_audio_in_browser);
+  is(result.computedVolume, 0, "Audio volume is 0 when muted");
+  is(result.computedMuted, true, "Audio is muted");
+}
+
+add_task(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [["media.useAudioChannelService.testing", true]],
+  });
+});
+
+add_task(async function test_page() {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:blank",
+    },
+    test_on_browser.bind(undefined, PAGE)
+  );
+});
+
+add_task(async function test_frame() {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:blank",
+    },
+    test_on_browser.bind(undefined, FRAME)
+  );
+});
+
+add_task(async function test_frame() {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:blank",
+    },
+    test_visibility.bind(undefined, PAGE)
+  );
+});
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaplayback_audibility_change.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaplayback_audibility_change.js
new file mode 100644
index 000000000..6c0c9de2b
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_mediaplayback_audibility_change.js
@@ -0,0 +1,258 @@
+/**
+ * When media changes its audible state, the sound indicator should be
+ * updated as well, which should appear only when web audio is audible.
+ */
+add_task(async function testUpdateSoundIndicatorWhenMediaPlaybackChanges() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+  await initMediaPlaybackDocument(tab, "audio.ogg");
+
+  info(`sound indicator should appear when audible audio starts playing`);
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`sound indicator should disappear when audio stops playing`);
+  await pauseMedia(tab);
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testUpdateSoundIndicatorWhenMediaBecomeSilent() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+  await initMediaPlaybackDocument(tab, "audioEndedDuringPlaying.webm");
+
+  info(`sound indicator should appear when audible audio starts playing`);
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`sound indicator should disappear when audio becomes silent`);
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testSoundIndicatorWouldWorkForMediaWithoutPreload() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+  await initMediaPlaybackDocument(tab, "audio.ogg", { preload: "none" });
+
+  info(`sound indicator should appear when audible audio starts playing`);
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`sound indicator should disappear when audio stops playing`);
+  await pauseMedia(tab);
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testSoundIndicatorShouldDisappearAfterTabNavigation() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+  await initMediaPlaybackDocument(tab, "audio.ogg");
+
+  info(`sound indicator should appear when audible audio starts playing`);
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`sound indicator should disappear after navigating tab to blank page`);
+  BrowserTestUtils.startLoadingURIString(tab.linkedBrowser, "about:blank");
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testSoundIndicatorForAudioStream() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+  await initMediaStreamPlaybackDocument(tab);
+
+  info(`sound indicator should appear when audible audio starts playing`);
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`sound indicator should disappear when audio stops playing`);
+  await pauseMedia(tab);
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testPerformPlayOnMediaLoadingNewSource() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+  await initMediaPlaybackDocument(tab, "audio.ogg");
+
+  info(`sound indicator should appear when audible audio starts playing`);
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`sound indicator should disappear when audio stops playing`);
+  await pauseMedia(tab);
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info(`reset media src and play it again should make sound indicator appear`);
+  await assignNewSourceForAudio(tab, "audio.ogg");
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testSoundIndicatorShouldDisappearWhenAbortingMedia() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+  await initMediaPlaybackDocument(tab, "audio.ogg");
+
+  info(`sound indicator should appear when audible audio starts playing`);
+  await playMedia(tab);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`sound indicator should disappear when aborting audio source`);
+  await assignNewSourceForAudio(tab, "");
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testNoSoundIndicatorForMediaWithoutAudioTrack() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab({ needObserver: true });
+  await initMediaPlaybackDocument(tab, "noaudio.webm", { createVideo: true });
+
+  info(`no sound indicator should show for playing media without audio track`);
+  await playMedia(tab, { resolveOnTimeupdate: true });
+  ok(!tab.observer.hasEverUpdated(), "didn't ever update sound indicator");
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testSoundIndicatorWhenChangingMediaMuted() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab({ needObserver: true });
+  await initMediaPlaybackDocument(tab, "audio.ogg", { muted: true });
+
+  info(`no sound indicator should show for playing muted media`);
+  await playMedia(tab, { resolveOnTimeupdate: true });
+  ok(!tab.observer.hasEverUpdated(), "didn't ever update sound indicator");
+
+  info(`unmuted media should make sound indicator appear`);
+  await Promise.all([
+    waitForTabSoundIndicatorAppears(tab),
+    updateMedia(tab, { muted: false }),
+  ]);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testSoundIndicatorWhenChangingMediaVolume() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab({ needObserver: true });
+  await initMediaPlaybackDocument(tab, "audio.ogg", { volume: 0.0 });
+
+  info(`no sound indicator should show for playing volume zero media`);
+  await playMedia(tab, { resolveOnTimeupdate: true });
+  ok(!tab.observer.hasEverUpdated(), "didn't ever update sound indicator");
+
+  info(`unmuted media by setting volume should make sound indicator appear`);
+  await Promise.all([
+    waitForTabSoundIndicatorAppears(tab),
+    updateMedia(tab, { volume: 1.0 }),
+  ]);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+/**
+ * Following are helper functions
+ */
+function initMediaPlaybackDocument(
+  tab,
+  fileName,
+  { preload, createVideo, muted = false, volume = 1.0 } = {}
+) {
+  return SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [fileName, preload, createVideo, muted, volume],
+    // eslint-disable-next-line no-shadow
+    async (fileName, preload, createVideo, muted, volume) => {
+      if (createVideo) {
+        content.media = content.document.createElement("video");
+      } else {
+        content.media = content.document.createElement("audio");
+      }
+      if (preload) {
+        content.media.preload = preload;
+      }
+      content.media.muted = muted;
+      content.media.volume = volume;
+      content.media.src = fileName;
+    }
+  );
+}
+
+function initMediaStreamPlaybackDocument(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], async _ => {
+    content.media = content.document.createElement("audio");
+    content.media.srcObject =
+      new content.AudioContext().createMediaStreamDestination().stream;
+  });
+}
+
+function playMedia(tab, { resolveOnTimeupdate } = {}) {
+  return SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [resolveOnTimeupdate],
+    // eslint-disable-next-line no-shadow
+    async resolveOnTimeupdate => {
+      await content.media.play();
+      if (resolveOnTimeupdate) {
+        await new Promise(r => (content.media.ontimeupdate = r));
+      }
+    }
+  );
+}
+
+function pauseMedia(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], async _ => {
+    content.media.pause();
+  });
+}
+
+function assignNewSourceForAudio(tab, fileName) {
+  // eslint-disable-next-line no-shadow
+  return SpecialPowers.spawn(tab.linkedBrowser, [fileName], async fileName => {
+    content.media.src = "";
+    content.media.removeAttribute("src");
+    content.media.src = fileName;
+  });
+}
+
+function updateMedia(tab, { muted, volume } = {}) {
+  return SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [muted, volume],
+    // eslint-disable-next-line no-shadow
+    (muted, volume) => {
+      if (muted != undefined) {
+        content.media.muted = muted;
+      }
+      if (volume != undefined) {
+        content.media.volume = volume;
+      }
+    }
+  );
+}
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_mute.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_mute.js
new file mode 100644
index 000000000..826e06c3d
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_mute.js
@@ -0,0 +1,19 @@
+const PAGE = "data:text/html,page";
+
+function test_on_browser(browser) {
+  ok(!browser.audioMuted, "Audio should not be muted by default");
+  browser.mute();
+  ok(browser.audioMuted, "Audio should be muted now");
+  browser.unmute();
+  ok(!browser.audioMuted, "Audio should be unmuted now");
+}
+
+add_task(async function () {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: PAGE,
+    },
+    test_on_browser
+  );
+});
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_mute2.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_mute2.js
new file mode 100644
index 000000000..5e845454d
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_mute2.js
@@ -0,0 +1,32 @@
+const PAGE = "data:text/html,page";
+
+async function test_on_browser(browser) {
+  ok(!browser.audioMuted, "Audio should not be muted by default");
+  browser.mute();
+  ok(browser.audioMuted, "Audio should be muted now");
+
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: PAGE,
+    },
+    test_on_browser2
+  );
+
+  browser.unmute();
+  ok(!browser.audioMuted, "Audio should be unmuted now");
+}
+
+function test_on_browser2(browser) {
+  ok(!browser.audioMuted, "Audio should not be muted by default");
+}
+
+add_task(async function () {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: PAGE,
+    },
+    test_on_browser
+  );
+});
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_mute_webAudio.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_mute_webAudio.js
new file mode 100644
index 000000000..abcbbf9ce
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_mute_webAudio.js
@@ -0,0 +1,72 @@
+// The tab closing code leaves an uncaught rejection. This test has been
+// whitelisted until the issue is fixed.
+if (!gMultiProcessBrowser) {
+  const { PromiseTestUtils } = ChromeUtils.importESModule(
+    "resource://testing-common/PromiseTestUtils.sys.mjs"
+  );
+  PromiseTestUtils.expectUncaughtRejection(/is no longer, usable/);
+}
+
+const PAGE = GetTestWebBasedURL("file_webAudio.html");
+
+function start_webAudio() {
+  var startButton = content.document.getElementById("start");
+  if (!startButton) {
+    ok(false, "Can't get the start button!");
+  }
+
+  startButton.click();
+}
+
+function stop_webAudio() {
+  var stopButton = content.document.getElementById("stop");
+  if (!stopButton) {
+    ok(false, "Can't get the stop button!");
+  }
+
+  stopButton.click();
+}
+
+add_task(async function setup_test_preference() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["media.useAudioChannelService.testing", true],
+      ["media.block-autoplay-until-in-foreground", true],
+    ],
+  });
+});
+
+add_task(async function mute_web_audio() {
+  info("- open new tab -");
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    window.gBrowser,
+    "about:blank"
+  );
+  BrowserTestUtils.startLoadingURIString(tab.linkedBrowser, PAGE);
+  await BrowserTestUtils.browserLoaded(tab.linkedBrowser);
+
+  info("- tab should be audible -");
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info("- mute browser -");
+  ok(!tab.linkedBrowser.audioMuted, "Audio should not be muted by default");
+  await clickIcon(tab.audioButton);
+  ok(tab.linkedBrowser.audioMuted, "Audio should be muted now");
+
+  info("- stop web audip -");
+  await SpecialPowers.spawn(tab.linkedBrowser, [], stop_webAudio);
+
+  info("- start web audio -");
+  await SpecialPowers.spawn(tab.linkedBrowser, [], start_webAudio);
+
+  info("- unmute browser -");
+  ok(tab.linkedBrowser.audioMuted, "Audio should be muted now");
+  await clickIcon(tab.audioButton);
+  ok(!tab.linkedBrowser.audioMuted, "Audio should be unmuted now");
+
+  info("- tab should be audible -");
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info("- remove tab -");
+  BrowserTestUtils.removeTab(tab);
+});
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_sound_indicator_silent_video.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_sound_indicator_silent_video.js
new file mode 100644
index 000000000..882a9bc80
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_sound_indicator_silent_video.js
@@ -0,0 +1,95 @@
+const SILENT_PAGE = GetTestWebBasedURL("file_silentAudioTrack.html");
+const ALMOST_SILENT_PAGE = GetTestWebBasedURL(
+  "file_almostSilentAudioTrack.html"
+);
+
+function check_audio_playing_state(isPlaying) {
+  let autoPlay = content.document.getElementById("autoplay");
+  if (!autoPlay) {
+    ok(false, "Can't get the audio element!");
+  }
+
+  is(
+    autoPlay.paused,
+    !isPlaying,
+    "The playing state of autoplay audio is correct."
+  );
+
+  // wait for a while to make sure the video is playing and related event has
+  // been dispatched (if any).
+  let PLAYING_TIME_SEC = 0.5;
+  Assert.less(
+    PLAYING_TIME_SEC,
+    autoPlay.duration,
+    "The playing time is valid."
+  );
+
+  return new Promise(resolve => {
+    autoPlay.ontimeupdate = function () {
+      if (autoPlay.currentTime > PLAYING_TIME_SEC) {
+        resolve();
+      }
+    };
+  });
+}
+
+add_task(async function should_not_show_sound_indicator_for_silent_video() {
+  info("- open new foreground tab -");
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    window.gBrowser,
+    "about:blank"
+  );
+
+  info("- tab should not have sound indicator before playing silent video -");
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("- loading autoplay silent video -");
+  BrowserTestUtils.startLoadingURIString(tab.linkedBrowser, SILENT_PAGE);
+  await BrowserTestUtils.browserLoaded(tab.linkedBrowser);
+  await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [true],
+    check_audio_playing_state
+  );
+
+  info("- tab should not have sound indicator after playing silent video -");
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info("- remove tab -");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(
+  async function should_not_show_sound_indicator_for_almost_silent_video() {
+    info("- open new foreground tab -");
+    let tab = await BrowserTestUtils.openNewForegroundTab(
+      window.gBrowser,
+      "about:blank"
+    );
+
+    info(
+      "- tab should not have sound indicator before playing almost silent video -"
+    );
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info("- loading autoplay almost silent video -");
+    BrowserTestUtils.startLoadingURIString(
+      tab.linkedBrowser,
+      ALMOST_SILENT_PAGE
+    );
+    await BrowserTestUtils.browserLoaded(tab.linkedBrowser);
+    await SpecialPowers.spawn(
+      tab.linkedBrowser,
+      [true],
+      check_audio_playing_state
+    );
+
+    info(
+      "- tab should not have sound indicator after playing almost silent video -"
+    );
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info("- remove tab -");
+    BrowserTestUtils.removeTab(tab);
+  }
+);
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_webAudio_hideSoundPlayingIcon.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_webAudio_hideSoundPlayingIcon.js
new file mode 100644
index 000000000..be40f6e14
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_webAudio_hideSoundPlayingIcon.js
@@ -0,0 +1,60 @@
+/**
+ * This test is used to ensure the 'sound-playing' icon would not disappear after
+ * sites call AudioContext.resume().
+ */
+"use strict";
+
+function setup_test_preference() {
+  return SpecialPowers.pushPrefEnv({
+    set: [
+      ["media.useAudioChannelService.testing", true],
+      ["browser.tabs.delayHidingAudioPlayingIconMS", 0],
+    ],
+  });
+}
+
+async function resumeAudioContext() {
+  const ac = content.ac;
+  await ac.resume();
+  ok(true, "AudioContext is resumed.");
+}
+
+async function testResumeRunningAudioContext() {
+  info(`- create new tab -`);
+  const tab = await BrowserTestUtils.openNewForegroundTab(
+    window.gBrowser,
+    "about:blank"
+  );
+  const browser = tab.linkedBrowser;
+
+  info(`- create audio context -`);
+  // We want the same audio context to be used across different content tasks.
+  await SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    content.ac = new content.AudioContext();
+    const ac = content.ac;
+    const dest = ac.destination;
+    const osc = ac.createOscillator();
+    osc.connect(dest);
+    osc.start();
+  });
+
+  info(`- wait for 'sound-playing' icon showing -`);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`- resume AudioContext -`);
+  await SpecialPowers.spawn(browser, [], resumeAudioContext);
+
+  info(`- 'sound-playing' icon should still exist -`);
+  await waitForTabSoundIndicatorAppears(tab);
+
+  info(`- remove tab -`);
+  await BrowserTestUtils.removeTab(tab);
+}
+
+add_task(async function start_test() {
+  info("- setup test preference -");
+  await setup_test_preference();
+
+  info("- start testing -");
+  await testResumeRunningAudioContext();
+});
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_webAudio_silentData.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_webAudio_silentData.js
new file mode 100644
index 000000000..5831d3c0c
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_webAudio_silentData.js
@@ -0,0 +1,57 @@
+/**
+ * This test is used to make sure we won't show the sound indicator for silent
+ * web audio.
+ */
+/* eslint-disable mozilla/no-arbitrary-setTimeout */
+"use strict";
+
+async function waitUntilAudioContextStarts() {
+  const ac = content.ac;
+  if (ac.state == "running") {
+    return;
+  }
+
+  await new Promise(resolve => {
+    ac.onstatechange = () => {
+      if (ac.state == "running") {
+        ac.onstatechange = null;
+        resolve();
+      }
+    };
+  });
+}
+
+add_task(async function testSilentAudioContext() {
+  info(`- create new tab -`);
+  const tab = await BrowserTestUtils.openNewForegroundTab(
+    window.gBrowser,
+    "about:blank"
+  );
+  const browser = tab.linkedBrowser;
+
+  info(`- create audio context -`);
+  // We want the same audio context to be used across different content tasks
+  await SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    content.ac = new content.AudioContext();
+    const ac = content.ac;
+    const dest = ac.destination;
+    const source = new content.OscillatorNode(content.ac);
+    const gain = new content.GainNode(content.ac);
+    gain.gain.value = 0.0;
+    source.connect(gain).connect(dest);
+    source.start();
+  });
+  info(`- check AudioContext's state -`);
+  await SpecialPowers.spawn(browser, [], waitUntilAudioContextStarts);
+  ok(true, `AudioContext is running.`);
+
+  info(`- should not show sound indicator -`);
+  // If we do the next step too early, then we can't make sure whether that the
+  // reason of no showing sound indicator is because of silent web audio, or
+  // because the indicator is just not showing yet.
+  await new Promise(r => setTimeout(r, 1000));
+  await waitForTabSoundIndicatorDisappears(tab);
+
+  info(`- remove tab -`);
+  await BrowserTestUtils.removeTab(tab);
+});
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/browser_webaudio_audibility_change.js b/src/zen/tests/mochitests/tabMediaIndicator/browser_webaudio_audibility_change.js
new file mode 100644
index 000000000..7cdc87020
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/browser_webaudio_audibility_change.js
@@ -0,0 +1,172 @@
+const EMPTY_PAGE_URL = GetTestWebBasedURL("file_empty.html");
+
+/**
+ * When web audio changes its audible state, the sound indicator should be
+ * updated as well, which should appear only when web audio is audible.
+ */
+add_task(
+  async function testWebAudioAudibilityWouldAffectTheAppearenceOfTabSoundIndicator() {
+    info(`sound indicator should appear when web audio plays audible sound`);
+    const tab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      EMPTY_PAGE_URL
+    );
+    await initWebAudioDocument(tab);
+    await waitForTabSoundIndicatorAppears(tab);
+
+    info(`sound indicator should disappear when suspending web audio`);
+    await suspendWebAudio(tab);
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info(`sound indicator should appear when resuming web audio`);
+    await resumeWebAudio(tab);
+    await waitForTabSoundIndicatorAppears(tab);
+
+    info(`sound indicator should disappear when muting web audio by docShell`);
+    await muteWebAudioByDocShell(tab);
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info(`sound indicator should appear when unmuting web audio by docShell`);
+    await unmuteWebAudioByDocShell(tab);
+    await waitForTabSoundIndicatorAppears(tab);
+
+    info(`sound indicator should disappear when muting web audio by gain node`);
+    await muteWebAudioByGainNode(tab);
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info(`sound indicator should appear when unmuting web audio by gain node`);
+    await unmuteWebAudioByGainNode(tab);
+    await waitForTabSoundIndicatorAppears(tab);
+
+    info(`sound indicator should disappear when closing web audio`);
+    await closeWebAudio(tab);
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info("remove tab");
+    BrowserTestUtils.removeTab(tab);
+  }
+);
+
+add_task(async function testSoundIndicatorShouldDisappearAfterTabNavigation() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab();
+
+  info(`sound indicator should appear when audible web audio starts playing`);
+  await Promise.all([
+    initWebAudioDocument(tab),
+    waitForTabSoundIndicatorAppears(tab),
+  ]);
+
+  info(`sound indicator should disappear after navigating tab to blank page`);
+  await Promise.all([
+    BrowserTestUtils.startLoadingURIString(tab.linkedBrowser, "about:blank"),
+    waitForTabSoundIndicatorDisappears(tab),
+  ]);
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(
+  async function testSoundIndicatorShouldDisappearAfterWebAudioBecomesSilent() {
+    info("create a tab loading media document");
+    const tab = await createBlankForegroundTab();
+
+    info(`sound indicator should appear when audible web audio starts playing`);
+    await Promise.all([
+      initWebAudioDocument(tab, { duration: 0.1 }),
+      waitForTabSoundIndicatorAppears(tab),
+    ]);
+
+    info(`sound indicator should disappear after web audio become silent`);
+    await waitForTabSoundIndicatorDisappears(tab);
+
+    info("remove tab");
+    BrowserTestUtils.removeTab(tab);
+  }
+);
+
+add_task(async function testNoSoundIndicatorWhenSimplyCreateAudioContext() {
+  info("create a tab loading media document");
+  const tab = await createBlankForegroundTab({ needObserver: true });
+
+  info(`sound indicator should not appear when simply create an AudioContext`);
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async _ => {
+    content.ac = new content.AudioContext();
+    while (content.ac.state != "running") {
+      info(`wait until web audio starts running`);
+      await new Promise(r => (content.ac.onstatechange = r));
+    }
+  });
+  ok(!tab.observer.hasEverUpdated(), "didn't ever update sound indicator");
+
+  info("remove tab");
+  BrowserTestUtils.removeTab(tab);
+});
+
+/**
+ * Following are helper functions
+ */
+function initWebAudioDocument(tab, { duration } = {}) {
+  // eslint-disable-next-line no-shadow
+  return SpecialPowers.spawn(tab.linkedBrowser, [duration], async duration => {
+    content.ac = new content.AudioContext();
+    const ac = content.ac;
+    const dest = ac.destination;
+    const source = new content.OscillatorNode(ac);
+    source.start(ac.currentTime);
+    if (duration != undefined) {
+      source.stop(ac.currentTime + duration);
+    }
+    // create a gain node for future muting/unmuting
+    content.gainNode = ac.createGain();
+    source.connect(content.gainNode);
+    content.gainNode.connect(dest);
+    while (ac.state != "running") {
+      info(`wait until web audio starts running`);
+      await new Promise(r => (ac.onstatechange = r));
+    }
+  });
+}
+
+function suspendWebAudio(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], async _ => {
+    await content.ac.suspend();
+  });
+}
+
+function resumeWebAudio(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], async _ => {
+    await content.ac.resume();
+  });
+}
+
+function closeWebAudio(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], async _ => {
+    await content.ac.close();
+  });
+}
+
+function muteWebAudioByDocShell(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+    content.docShell.allowMedia = false;
+  });
+}
+
+function unmuteWebAudioByDocShell(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+    content.docShell.allowMedia = true;
+  });
+}
+
+function muteWebAudioByGainNode(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+    content.gainNode.gain.setValueAtTime(0, content.ac.currentTime);
+  });
+}
+
+function unmuteWebAudioByGainNode(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+    content.gainNode.gain.setValueAtTime(1.0, content.ac.currentTime);
+  });
+}
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_almostSilentAudioTrack.html b/src/zen/tests/mochitests/tabMediaIndicator/file_almostSilentAudioTrack.html
new file mode 100644
index 000000000..3ce9a68b9
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_almostSilentAudioTrack.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<head>
+  <meta content="text/html;charset=utf-8" http-equiv="Content-Type">
+  <meta content="utf-8" http-equiv="encoding">
+</head>
+<body>
+<video id="autoplay" src="almostSilentAudioTrack.webm"></video>
+<script type="text/javascript">
+
+// In linux debug on try server, sometimes the download process would fail, so
+// we can't activate the "auto-play" or playing after receving "oncanplay".
+// Therefore, we just call play here.
+var video = document.getElementById("autoplay");
+video.loop = true;
+video.play();
+
+</script>
+</body>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_autoplay_media.html b/src/zen/tests/mochitests/tabMediaIndicator/file_autoplay_media.html
new file mode 100644
index 000000000..f0dcfdab5
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_autoplay_media.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>autoplay media page</title>
+</head>
+<body>
+<video id="video" src="gizmo.mp4" loop autoplay></video>
+</body>
+</html>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_empty.html b/src/zen/tests/mochitests/tabMediaIndicator/file_empty.html
new file mode 100644
index 000000000..13d5eeee7
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_empty.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>empty page</title>
+</head>
+<body>
+</body>
+</html>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlayback.html b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlayback.html
new file mode 100644
index 000000000..5df0bc154
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlayback.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<script type="text/javascript">
+var audio = new Audio();
+audio.oncanplay = function() {
+  audio.oncanplay = null;
+  audio.play();
+};
+audio.src = "audio.ogg";
+</script>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlayback2.html b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlayback2.html
new file mode 100644
index 000000000..890b494a0
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlayback2.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<body>
+<script type="text/javascript">
+var audio = new Audio();
+audio.oncanplay = function() {
+  audio.oncanplay = null;
+  audio.play();
+};
+audio.src = "audio.ogg";
+audio.loop = true;
+audio.id = "v";
+document.body.appendChild(audio);
+</script>
+</body>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlaybackFrame.html b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlaybackFrame.html
new file mode 100644
index 000000000..119db62ec
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlaybackFrame.html
@@ -0,0 +1,2 @@
+<!DOCTYPE html>
+<iframe src="file_mediaPlayback.html"></iframe>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlaybackFrame2.html b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlaybackFrame2.html
new file mode 100644
index 000000000..d96a4cd4e
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_mediaPlaybackFrame2.html
@@ -0,0 +1,2 @@
+<!DOCTYPE html>
+<iframe src="file_mediaPlayback2.html"></iframe>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_silentAudioTrack.html b/src/zen/tests/mochitests/tabMediaIndicator/file_silentAudioTrack.html
new file mode 100644
index 000000000..afdf2c529
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_silentAudioTrack.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<head>
+  <meta content="text/html;charset=utf-8" http-equiv="Content-Type">
+  <meta content="utf-8" http-equiv="encoding">
+</head>
+<body>
+<video id="autoplay" src="silentAudioTrack.webm"></video>
+<script type="text/javascript">
+
+// In linux debug on try server, sometimes the download process would fail, so
+// we can't activate the "auto-play" or playing after receving "oncanplay".
+// Therefore, we just call play here.
+var video = document.getElementById("autoplay");
+video.loop = true;
+video.play();
+
+</script>
+</body>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/file_webAudio.html b/src/zen/tests/mochitests/tabMediaIndicator/file_webAudio.html
new file mode 100644
index 000000000..f6fb5e7c0
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/file_webAudio.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<head>
+  <meta content="text/html;charset=utf-8" http-equiv="Content-Type">
+  <meta content="utf-8" http-equiv="encoding">
+</head>
+<body>
+<pre id=state></pre>
+<button id="start" onclick="start_webaudio()">Start</button>
+<button id="stop" onclick="stop_webaudio()">Stop</button>
+<script type="text/javascript">
+  var ac = new AudioContext();
+  var dest = ac.destination;
+  var osc = ac.createOscillator();
+  osc.connect(dest);
+  osc.start();
+  document.querySelector("pre").innerText = ac.state;
+  ac.onstatechange = function() {
+    document.querySelector("pre").innerText = ac.state;
+  }
+
+  function start_webaudio() {
+    ac.resume();
+  }
+
+  function stop_webaudio() {
+    ac.suspend();
+  }
+</script>
+</body>
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/gizmo.mp4 b/src/zen/tests/mochitests/tabMediaIndicator/gizmo.mp4
new file mode 100644
index 000000000..87efad5ad
Binary files /dev/null and b/src/zen/tests/mochitests/tabMediaIndicator/gizmo.mp4 differ
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/head.js b/src/zen/tests/mochitests/tabMediaIndicator/head.js
new file mode 100644
index 000000000..8d58339a2
--- /dev/null
+++ b/src/zen/tests/mochitests/tabMediaIndicator/head.js
@@ -0,0 +1,165 @@
+/**
+ * Global variables for testing.
+ */
+const gEMPTY_PAGE_URL = GetTestWebBasedURL("file_empty.html");
+
+/**
+ * Return a web-based URL for a given file based on the testing directory.
+ *
+ * @param {string} fileName
+ *        file that caller wants its web-based url
+ * @param {boolean} cors [optional]
+ *        if set, then return a url with different origin
+ */
+function GetTestWebBasedURL(fileName, cors = false) {
+  // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+  // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+  const origin = cors ? "http://example.org" : "http://example.com";
+  return (
+    getRootDirectory(gTestPath).replace("chrome://mochitests/content", origin) +
+    fileName
+  );
+}
+
+/**
+ * Wait until tab sound indicator appears on the given tab.
+ *
+ * @param {tabbrowser} tab
+ *        given tab where tab sound indicator should appear
+ */
+async function waitForTabSoundIndicatorAppears(tab) {
+  if (!tab.soundPlaying) {
+    info("Tab sound indicator doesn't appear yet");
+    await BrowserTestUtils.waitForEvent(
+      tab,
+      "TabAttrModified",
+      false,
+      event => {
+        return event.detail.changed.includes("soundplaying");
+      }
+    );
+  }
+  ok(tab.soundPlaying, "Tab sound indicator appears");
+}
+
+/**
+ * Wait until tab sound indicator disappears on the given tab.
+ *
+ * @param {tabbrowser} tab
+ *        given tab where tab sound indicator should disappear
+ */
+async function waitForTabSoundIndicatorDisappears(tab) {
+  if (tab.soundPlaying) {
+    info("Tab sound indicator doesn't disappear yet");
+    await BrowserTestUtils.waitForEvent(
+      tab,
+      "TabAttrModified",
+      false,
+      event => {
+        return event.detail.changed.includes("soundplaying");
+      }
+    );
+  }
+  ok(!tab.soundPlaying, "Tab sound indicator disappears");
+}
+
+/**
+ * Return a new foreground tab loading with an empty file.
+ *
+ * @param {boolean} needObserver
+ *        If true, sets an observer property on the returned tab. This property
+ *        exposes `hasEverUpdated()` which will return a bool indicating if the
+ *        sound indicator has ever updated.
+ */
+async function createBlankForegroundTab({ needObserver } = {}) {
+  const tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    gEMPTY_PAGE_URL
+  );
+  if (needObserver) {
+    tab.observer = createSoundIndicatorObserver(tab);
+  }
+  return tab;
+}
+
+function createSoundIndicatorObserver(tab) {
+  let hasEverUpdated = false;
+  let listener = event => {
+    if (event.detail.changed.includes("soundplaying")) {
+      hasEverUpdated = true;
+    }
+  };
+  tab.addEventListener("TabAttrModified", listener);
+  return {
+    hasEverUpdated: () => {
+      tab.removeEventListener("TabAttrModified", listener);
+      return hasEverUpdated;
+    },
+  };
+}
+
+/**
+ * Sythesize mouse hover on the given icon, which would sythesize `mouseover`
+ * and `mousemove` event on that. Return a promise that will be resolved when
+ * the tooptip element shows.
+ *
+ * @param {tab icon} icon
+ *        the icon on which we want to mouse hover
+ * @param {tooltip element} tooltip
+ *        the tab tooltip elementss
+ */
+function hoverIcon(icon, tooltip) {
+  disableNonTestMouse(true);
+
+  if (!tooltip) {
+    tooltip = document.getElementById("tabbrowser-tab-tooltip");
+  }
+
+  let popupShownPromise = BrowserTestUtils.waitForEvent(tooltip, "popupshown");
+  EventUtils.synthesizeMouse(icon, 1, 1, { type: "mouseover" });
+  EventUtils.synthesizeMouse(icon, 2, 2, { type: "mousemove" });
+  EventUtils.synthesizeMouse(icon, 3, 3, { type: "mousemove" });
+  EventUtils.synthesizeMouse(icon, 4, 4, { type: "mousemove" });
+  return popupShownPromise;
+}
+
+/**
+ * Leave mouse from the given icon, which would sythesize `mouseout`
+ * and `mousemove` event on that.
+ *
+ * @param {tab icon} icon
+ *        the icon on which we want to mouse hover
+ * @param {tooltip element} tooltip
+ *        the tab tooltip elementss
+ */
+function leaveIcon(icon) {
+  EventUtils.synthesizeMouse(icon, 0, 0, { type: "mouseout" });
+  EventUtils.synthesizeMouseAtCenter(document.documentElement, {
+    type: "mousemove",
+  });
+  EventUtils.synthesizeMouseAtCenter(document.documentElement, {
+    type: "mousemove",
+  });
+  EventUtils.synthesizeMouseAtCenter(document.documentElement, {
+    type: "mousemove",
+  });
+
+  disableNonTestMouse(false);
+}
+
+/**
+ * Sythesize mouse click on the given icon.
+ *
+ * @param {tab icon} icon
+ *        the icon on which we want to mouse hover
+ */
+async function clickIcon(icon) {
+  await hoverIcon(icon);
+  EventUtils.synthesizeMouseAtCenter(icon, { button: 0 });
+  leaveIcon(icon);
+}
+
+function disableNonTestMouse(disable) {
+  let utils = window.windowUtils;
+  utils.disableNonTestMouseEvents(disable);
+}
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/noaudio.webm b/src/zen/tests/mochitests/tabMediaIndicator/noaudio.webm
new file mode 100644
index 000000000..9207017fb
Binary files /dev/null and b/src/zen/tests/mochitests/tabMediaIndicator/noaudio.webm differ
diff --git a/src/zen/tests/mochitests/tabMediaIndicator/silentAudioTrack.webm b/src/zen/tests/mochitests/tabMediaIndicator/silentAudioTrack.webm
new file mode 100644
index 000000000..8e08a86c4
Binary files /dev/null and b/src/zen/tests/mochitests/tabMediaIndicator/silentAudioTrack.webm differ
diff --git a/src/zen/tests/moz.build b/src/zen/tests/moz.build
index 57e3d564a..c63e29a55 100644
--- a/src/zen/tests/moz.build
+++ b/src/zen/tests/moz.build
@@ -8,6 +8,7 @@ BROWSER_CHROME_MANIFESTS += [
     "folders/browser.toml",
     "glance/browser.toml",
     "live-folders/browser.toml",
+    "media/browser.toml",
     "pinned/browser.toml",
     "popover/browser.toml",
     "spaces/browser.toml",