diff --git a/toolkit/content/xul.css b/toolkit/content/xul.css
index 57dd6042d2620dd64c55e0e966913047a6c3502f..40d016a0a13596439046e2bbcfa59daa30f10b2d 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,
 tabpanels > .split-view-splitter,
-deck > .deck-selected {
+deck > .deck-selected,
+tabpanels > [zen-split="true"] {
   -moz-subtree-hidden-only-visually: 0;
   visibility: inherit;
 }