diff --git a/browser/themes/shared/tabbrowser/ctrlTab.css b/browser/themes/shared/tabbrowser/ctrlTab.css
index 50045ec27abcde91d5aea12fc7faaefbddf50229..f4e98dce5195ff3298fb98714d56cf5d3bdaaf48 100644
--- a/browser/themes/shared/tabbrowser/ctrlTab.css
+++ b/browser/themes/shared/tabbrowser/ctrlTab.css
@@ -12,6 +12,7 @@
   --panel-color: white;
   --panel-border-color: transparent;
   --panel-padding: 20px 10px 10px;
+  --panel-shadow-margin: 0;
 }
 
 @media (-moz-platform: macos) {
