diff --git a/browser/themes/shared/tabbrowser/ctrlTab.css b/browser/themes/shared/tabbrowser/ctrlTab.css
index 259e11f3c9a761e158dc32a3ecb9ee90c11d27c6..c5e30314090fe8f33b37c809bcf871c7b8c4d3da 100644
--- a/browser/themes/shared/tabbrowser/ctrlTab.css
+++ b/browser/themes/shared/tabbrowser/ctrlTab.css
@@ -11,6 +11,7 @@
   --panel-border-color: transparent;
   --panel-padding: 20px 10px 10px;
   -moz-window-shadow: none;
+  --panel-shadow-margin: 0;
   @media not (-moz-platform: macos) {
     font-weight: bold;
   }