Rated 5 out of 5 stars

Please add overlay.css.
#main-window:not([customizing]) #TabsToolbar:not(:-moz-lwtheme) {background-image: none !important;}
This will help remove grandient at Australis tabs included with the classic menu. It will be more beautiful.

This review is for a previous version of the add-on (1.1.8.1-signed). 

Thanks for the suggestion.

Since there already is an option to remove the tab toolbars background, I will add this extra tweak to it.
Next beta/final (1.2.0) will contain this.