diff --git a/browser/themes/osx/browser.css b/browser/themes/osx/browser.css
index 8347d2b629d3..7ccaf3c674ac 100644
--- a/browser/themes/osx/browser.css
+++ b/browser/themes/osx/browser.css
@@ -25,6 +25,8 @@
   display: -moz-box;
   height: 2px;
   margin-top: -2px;
+  position: relative;
+  z-index: 2; /* navbar is at 1 */
 }
 
 #navigator-toolbox toolbarbutton:-moz-lwtheme {