Rated 1 out of 5 stars

per ShopsinMilwaukee el feb. 6, 2019 ·

Added it to Thunderbird 60.5.0 and it did nothing at all

This review is for a previous version of the add-on (1.7). 

per Paenglab (desenvolupador) a feb. 6, 2019 ·

Have you tried to right click on the main toolbar and then choose "Customize"? Then you can move the buttons you want to the left of the first tab.

Without customizing this extension does nothing.