Very useful addon Rated 4 out of 5 stars

But I think it would be much better to be able to customize the icon.

This review is for a previous version of the add-on (1.0.1-signed). 

This add-on offers no preferences, but you can override the current icon using custom code in Stylish add-on or userChrome.css.

I've added some info about that to main page.