The author has marked this style as obsolete.
I haven't had time to do more work on this but Greg S posted a better version here: http://forums.mozillazine.org/viewtopic.php?p=2524057#2524057




Styles the tabs in Page Info and Advanced Options like the default browser tabs. Tested with the default Firefox theme. Still needs some tweaking.
CSS adapted from chrome://global/skin/browser.css and chrome://global/skin/tabbox.css.
Very cool! Also, you can remove the @-moz-document rule and style all tabs in the browser like this, though doing that changes the main tabs a bit too.
excellent!!!!!!!!