diff --git a/browser/themes/shared/tabbrowser/ctrlTab.css b/browser/themes/shared/tabbrowser/ctrlTab.css
index 645467864db4a73b7addf3a57fa892beaf9a9614..46907c1ac8a10e8aba8ad82530269b660add550d 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) {
