diff --git a/browser/components/customizableui/CustomizableUI.sys.mjs b/browser/components/customizableui/CustomizableUI.sys.mjs
index 4aca0aa0c90603e09b58395debb62875c018a8cf..400ad196c846083001b36d27edec6885c6bde16d 100644
--- a/browser/components/customizableui/CustomizableUI.sys.mjs
+++ b/browser/components/customizableui/CustomizableUI.sys.mjs
@@ -14,6 +14,7 @@ ChromeUtils.defineESModuleGetters(lazy, {
   BrowserUsageTelemetry: "resource:///modules/BrowserUsageTelemetry.sys.mjs",
   CustomizableWidgets:
     "moz-src:///browser/components/customizableui/CustomizableWidgets.sys.mjs",
+  ZenCustomizableUI: "resource:///modules/ZenCustomizableUI.sys.mjs",
   HomePage: "resource:///modules/HomePage.sys.mjs",
   PanelMultiView:
     "moz-src:///browser/components/customizableui/PanelMultiView.sys.mjs",
@@ -348,7 +349,7 @@ var CustomizableUIInternal = {
       {
         type: CustomizableUI.TYPE_PANEL,
         defaultPlacements: [],
-        anchor: "unified-extensions-button",
+        anchor: "zen-site-data-icon-button",
       },
       false
     );
@@ -358,20 +359,15 @@ var CustomizableUIInternal = {
       "back-button",
       "forward-button",
       "stop-reload-button",
-      Services.policies.isAllowed("removeHomeButtonByDefault")
-        ? null
-        : "home-button",
       "spring",
       "vertical-spacer",
       "urlbar-container",
       "spring",
-      "downloads-button",
       AppConstants.MOZ_DEV_EDITION ? "developer-button" : null,
       lazy.ippEnabled ? "ipprotection-button" : null,
-      "fxa-toolbar-menu-button",
       lazy.resetPBMToolbarButtonEnabled ? "reset-pbm-toolbar-button" : null,
     ].filter(name => name);
-
+    lazy.ZenCustomizableUI.startup(this);
     this.registerArea(
       CustomizableUI.AREA_NAVBAR,
       {
@@ -379,8 +375,6 @@ var CustomizableUIInternal = {
         overflowable: true,
         defaultPlacements: navbarPlacements,
         verticalTabsDefaultPlacements: [
-          "firefox-view-button",
-          "alltabs-button",
         ],
         defaultCollapsed: false,
       },
@@ -404,10 +398,7 @@ var CustomizableUIInternal = {
       {
         type: CustomizableUI.TYPE_TOOLBAR,
         defaultPlacements: [
-          "firefox-view-button",
           "tabbrowser-tabs",
-          "new-tab-button",
-          "alltabs-button",
         ],
         verticalTabsDefaultPlacements: [],
         defaultCollapsed: null,
@@ -489,6 +480,7 @@ var CustomizableUIInternal = {
       CustomizableUI.AREA_NAVBAR,
       CustomizableUI.AREA_BOOKMARKS,
       CustomizableUI.AREA_TABSTRIP,
+      "zen-sidebar-top-buttons",
     ]);
     if (AppConstants.platform != "macosx") {
       toolbars.add(CustomizableUI.AREA_MENUBAR);
@@ -1265,6 +1257,9 @@ var CustomizableUIInternal = {
         placements = gPlacements.get(area);
       }
 
+      // remove "zen-sidebar-top-buttons" from the placements
+      placements = placements.filter(p => p != "zen-sidebar-top-buttons");
+
       // For toolbars that need it, mark as dirty.
       let defaultPlacements = areaProperties.get("defaultPlacements");
       if (
@@ -1772,7 +1767,6 @@ var CustomizableUIInternal = {
         lazy.log.info(
           "Widget " + aWidgetId + " not found, unable to remove from " + aArea
         );
-        continue;
       }
 
       this.notifyDOMChange(widgetNode, null, container, true, () => {
@@ -1782,7 +1776,7 @@ var CustomizableUIInternal = {
         // We also need to remove the panel context menu if it's there:
         this.ensureButtonContextMenu(widgetNode);
         if (gPalette.has(aWidgetId) || this.isSpecialWidget(aWidgetId)) {
-          container.removeChild(widgetNode);
+          widgetNode.remove();
         } else {
           window.gNavToolbox.palette.appendChild(widgetNode);
         }
@@ -1950,16 +1944,16 @@ var CustomizableUIInternal = {
         elem.setAttribute("skipintoolbarset", "true");
       }
     }
-
+    lazy.ZenCustomizableUI.init(aWindow);
     // Now register all the toolbars
     for (let area of CustomizableUI.areas) {
       let type = CustomizableUI.getAreaType(area);
-      if (type == CustomizableUI.TYPE_TOOLBAR) {
+      if (type == CustomizableUI.TYPE_TOOLBAR && !area.startsWith("zen-")) {
         let node = document.getElementById(area);
         this.registerToolbarNode(node);
       }
     }
-
+    lazy.ZenCustomizableUI.registerToolbarNodes(aWindow);
     // Handle initial state of vertical tabs.
     if (isVerticalTabs) {
       // Show the vertical tabs toolbar
@@ -2201,6 +2195,10 @@ var CustomizableUIInternal = {
    *   The identifier string of the area that aNode is being inserted into.
    */
   insertWidgetBefore(aNode, aNextNode, aContainer, aAreaId) {
+    if (aAreaId === CustomizableUI.AREA_NAVBAR && aNode.ownerGlobal.gZenVerticalTabsManager._hasSetSingleToolbar) {
+      aContainer = aNode.ownerDocument.getElementById("zen-sidebar-top-buttons-customization-target");
+      aAreaId = "zen-sidebar-top-buttons";
+    }
     this.notifyDOMChange(aNode, aNextNode, aContainer, false, () => {
       this.setLocationAttributes(aNode, aAreaId);
       aContainer.insertBefore(aNode, aNextNode);
@@ -4554,7 +4552,7 @@ var CustomizableUIInternal = {
    * For all registered areas, builds those areas to reflect the current
    * placement state of all widgets.
    */
-  _rebuildRegisteredAreas() {
+  _rebuildRegisteredAreas(zenDontRebuildCollapsed = false) {
     for (let [areaId, areaNodes] of gBuildAreas) {
       let placements = gPlacements.get(areaId);
       let isFirstChangedToolbar = true;
@@ -4565,7 +4563,7 @@ var CustomizableUIInternal = {
         if (area.get("type") == CustomizableUI.TYPE_TOOLBAR) {
           let defaultCollapsed = area.get("defaultCollapsed");
           let win = areaNode.ownerGlobal;
-          if (defaultCollapsed !== null) {
+          if (defaultCollapsed !== null && !zenDontRebuildCollapsed) {
             win.setToolbarVisibility(
               areaNode,
               typeof defaultCollapsed == "string"
@@ -5856,6 +5854,7 @@ export var CustomizableUI = {
   unregisterArea(aName, aDestroyPlacements) {
     CustomizableUIInternal.unregisterArea(aName, aDestroyPlacements);
   },
+  get zenInternalCU() { return CustomizableUIInternal; },
   /**
    * Add a widget to an area.
    * If the area to which you try to add is not known to CustomizableUI,
@@ -7819,7 +7818,9 @@ class OverflowableToolbar {
         );
 
         if (webExtList && CustomizableUI.isWebExtensionWidget(child.id)) {
+          if (webExtList.id !== "zen-overflow-extensions-list") {
           child.setAttribute("cui-anchorid", webExtButtonID);
+          }
           webExtList.insertBefore(child, webExtList.firstElementChild);
         } else {
           child.setAttribute("cui-anchorid", this.#defaultListButton.id);
@@ -7879,7 +7880,7 @@ class OverflowableToolbar {
         ) {
           continue;
         }
-        sum += parseFloat(style.marginLeft) + parseFloat(style.marginRight);
+        sum += parseFloat(style.marginLeft) + (win.gZenVerticalTabsManager._hasSetSingleToolbar ? Math.max(0, parseFloat(style.marginRight)) : parseFloat(style.marginRight));
         if (child != aExceptChild) {
           sum += getInlineSize(child);
         }
@@ -7903,11 +7904,11 @@ class OverflowableToolbar {
         parseFloat(style.paddingLeft) -
         parseFloat(style.paddingRight) -
         toolbarChildrenWidth;
-      targetWidth = getInlineSize(this.#target);
+      targetWidth = getInlineSize(this.#target) - ((win.gZenVerticalTabsManager._hasSetSingleToolbar && this.#target.id == 'zen-sidebar-top-buttons-customization-target') ? win.gZenVerticalTabsManager._topButtonsSeparatorElement.getBoundingClientRect().width : 0);
       targetChildrenWidth =
         this.#target == this.#toolbar
           ? toolbarChildrenWidth
-          : sumChildrenInlineSize(this.#target);
+          : sumChildrenInlineSize((win.gZenVerticalTabsManager._hasSetSingleToolbar && this.#target.id == 'nav-bar-customization-target') ? win.document.getElementById("zen-sidebar-top-buttons-customization-target") : this.#target, win.gZenVerticalTabsManager._topButtonsSeparatorElement);
     });
 
     lazy.log.debug(
@@ -7922,7 +7923,14 @@ class OverflowableToolbar {
       Math.max(targetWidth, targetChildrenWidth)
     );
     totalAvailWidth = Math.ceil(totalAvailWidth);
-    let isOverflowing = targetContentWidth > totalAvailWidth;
+    if (win.gZenVerticalTabsManager._hasSetSingleToolbar && this.#toolbar.id == 'nav-bar') return { isOverflowing: false, targetContentWidth, totalAvailWidth };
+    let isOverflowing = targetContentWidth + (win.gZenVerticalTabsManager._hasSetSingleToolbar ? 0.1 : 0) > totalAvailWidth;
+    if (win.gZenVerticalTabsManager._hasSetSingleToolbar &&
+      this.#target.id == 'zen-sidebar-top-buttons-customization-target' &&
+      Array.from(this.#target.children).filter(child => child.getAttribute("overflows") != "false").length == 1 &&
+      this.#overflowedInfo.size == 0) {
+      isOverflowing = false;
+    }
     return { isOverflowing, targetContentWidth, totalAvailWidth };
   }
 
@@ -7983,7 +7991,11 @@ class OverflowableToolbar {
             return;
           }
         }
-        if (totalAvailWidth <= minSize) {
+        let isLastItem = win.gZenVerticalTabsManager._hasSetSingleToolbar && 
+          this.#target.id == 'zen-sidebar-top-buttons-customization-target' && 
+          this.#overflowedInfo.size == 1 && 
+          !child.classList.contains('unified-extensions-item');
+        if (totalAvailWidth <= minSize && !isLastItem) {
           lazy.log.debug(
             `Need ${minSize} but width is ${totalAvailWidth} so bailing`
           );
@@ -8016,7 +8028,7 @@ class OverflowableToolbar {
         }
       }
       if (!inserted) {
-        this.#target.appendChild(child);
+        win.gZenVerticalTabsManager.appendCustomizableItem(this.#target, child, gPlacements.get(this.#toolbar.id));
       }
       child.removeAttribute("cui-anchorid");
       child.removeAttribute("overflowedItem");
@@ -8142,6 +8154,9 @@ class OverflowableToolbar {
    *   if no such list exists.
    */
   get #webExtList() {
+    if (this.#toolbar.getAttribute("addon-webext-overflowtarget") !== this.#webExtListRef?.id) {
+      this.#webExtListRef = null;
+    }
     if (!this.#webExtListRef) {
       let targetID = this.#toolbar.getAttribute("addon-webext-overflowtarget");
       if (!targetID) {
@@ -8153,6 +8168,9 @@ class OverflowableToolbar {
       let win = this.#toolbar.ownerGlobal;
       let { panel } = win.gUnifiedExtensions;
       this.#webExtListRef = panel.querySelector(`#${targetID}`);
+      if (!this.#webExtListRef) {
+        this.#webExtListRef = win.document.getElementById(targetID);
+      }
     }
     return this.#webExtListRef;
   }
@@ -8361,7 +8379,7 @@ class OverflowableToolbar {
         break;
       }
       case "mousedown": {
-        if (aEvent.button != 0) {
+        if (aEvent.button != 0 || this.#toolbar.id == "zen-sidebar-top-buttons") { // Fix https://github.com/zen-browser/desktop/issues/7718
           break;
         }
         if (aEvent.target == this.#defaultListButton) {
