Rated 4 out of 5 stars

Simple, and now indispensable for me as linux user. Thank you.

If you want the 'broom' gtk icon used by Firefox, use instead:
list-style-image: url("moz-icon://stock/gtk-clear?size=menu") !important;

This review is for a previous version of the add-on (1.3.1-signed.1-signed).