diff --git a/toolkit/content/xul.css b/toolkit/content/xul.css
index f730088432526521037a8933a6ee00af8c378f11..ef2bb2ecd364327a348602ff070814f653843081 100644
--- a/toolkit/content/xul.css
+++ b/toolkit/content/xul.css
@@ -446,7 +446,8 @@ deck > *|*:not(:-moz-native-anonymous) {
 }
 
 tabpanels > .deck-selected,
-deck > .deck-selected {
+deck > .deck-selected,
+tabpanels > [zen-split="true"] {
   -moz-subtree-hidden-only-visually: 0;
   visibility: inherit;
 }