Bug 569255 follow-up, removing redundant style rule

browser/themes/winstripe/browser/browser.css

@@ -1416,10 +1416,6 @@ richlistitem[type="action"][actiontype="switchtab"] > .ac-url-box > .ac-action-i
   -moz-image-region: rect(0, 48px, 16px, 32px);
 }
 
-#sidebar-header > .tabs-closebutton {
-  list-style-image: url("chrome://global/skin/icons/close.png");
-}
-
 toolbarbutton.chevron {
   list-style-image: url("chrome://global/skin/toolbar/chevron.gif") !important;
 }