diff --git a/toolkit/content/xul.css b/toolkit/content/xul.css
index db311601fb2c814139a66316e06707a56b7ac5cc..3a4cefcefe029d0054de0252fe8dead6dc248f59 100644
--- a/toolkit/content/xul.css
+++ b/toolkit/content/xul.css
@@ -463,7 +463,8 @@ deck > *|*:not(:-moz-native-anonymous) {
 tabpanels > .deck-selected,
 tabpanels > .split-view-panel-active,
 tabpanels > .split-view-splitter,
-deck > .deck-selected {
+deck > .deck-selected,
+tabpanels > [zen-split="true"] {
   -moz-subtree-hidden-only-visually: 0;
   visibility: inherit;
 }
