Rated 4 out of 5 stars

The icons are very nice, but the addon itself often doesn't start with Thunderbird, why?
In that case, I always have to turn the addon off and then on to load it.

This review is for a previous version of the add-on (3.5). 

I can't reproduce this, what other add-ons do you have installed?
You can try to clear the startup cache:
Help > More Troubleshooting Information > Clear startup cache...

Please use the Support E-mail address for bugs.