Rated 5 out of 5 stars

This is a very cool add-on. I found out about it through a newsfeed from How-To Geek (http://www.howtogeek.com/howto/4453/add-specialized-toolbar-buttons-to-firefox-the-easy-way/) That feed also includeda helper sites for this add-on to make one's own buttons:
http://codefisher.org/toolbar_button/toolbar_button_maker

This review is for a previous version of the add-on (0.6.0.8).