diff --git a/hosts/pinwheel/modules/firefox/default.nix b/hosts/pinwheel/modules/firefox/default.nix
index 35669ce..648711b 100644
--- a/hosts/pinwheel/modules/firefox/default.nix
+++ b/hosts/pinwheel/modules/firefox/default.nix
@@ -100,8 +100,8 @@ in
           };
 
           userChrome = ''
-            .tab-content {
-              border-top: solid #9400FF !important;
+            #main-window {
+              border: 2px solid #9400FF !important;
             }
           '';
         };