Rated 3 out of 5 stars

On opening it now requires to log-in into your Google account. After having logged in, you need anyway to keep that window open, or your connection will be cut off. In that case, I think the only solution is to close and re-open Thunderbird.
It's a good add-on, anyway.

This review is for a previous version of the add-on (3.1). 

I'd be interested to hear more about this via support. The login window should close itself after log in and it should be working then