--- a/browser/themes/osx/browser.css
+++ b/browser/themes/osx/browser.css
@@ -1430,17 +1430,18 @@ toolbar .toolbarbutton-1 > .toolbarbutto
 #zoom-out-button:-moz-locale-dir(rtl),
 #zoom-in-button:-moz-locale-dir(ltr) {
   border-top-left-radius: 0;
   border-bottom-left-radius: 0;
 }
 
 #zoom-controls[cui-areatype="toolbar"]:not([overflowedItem=true]) > #zoom-reset-button {
   min-width: 0;
-  margin: 0;
+  margin-left: 0;
+  margin-right: 0;
   -moz-box-orient: horizontal;
   -moz-box-align: center;
 }
 
 /* ----- FULLSCREEN WINDOW CONTROLS ----- */
 
 #minimize-button,
 #close-button,