Rated 4 out of 5 stars

I install and customize " Tab Utilities "

I drag a button to the toolbar.

Then I restart Firefox.

Customization becomes ineffective in " tab bar " and " tab contextmenu "

This review is for a previous version of the add-on (0.76.1-signed). 

I installed "Tab utilities" and I tried to drag all buttons to the tollbar with success... I got no problems and "Tab Utilities" works fine.