diff --git a/toolkit/content/xul.css b/toolkit/content/xul.css
index 134acec351c818eb824e2c98fa380d99ebaf8fac..3774893d98617634150f1f85568e212d98f9404c 100644
--- a/toolkit/content/xul.css
+++ b/toolkit/content/xul.css
@@ -468,7 +468,8 @@ 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;
 }
