Rated 4 out of 5 stars

It works fine, except for one thing. The login isn't remembered. Every time Thunderbird is started (effectively once a day for me) I get two Google login screens (I assume once for calendar, and another for tasks, althouth it's the same account..)

Otherwise, good plugin.

/edit
Thanks for the quick response!
Seems to have worked. Let's see for how long, but for now, somehow, re-adding the calendar fixed it. I restarted TB and it doesn't ask for my login again. I'll increase my rating ;)

This review is for a previous version of the add-on (1.0.4). 

Can you try unsubscribing from calendar and tasks lists, then re-subscribing and making sure you enter one email address when prompted? I've heard of this issue, but I haven't been able to reproduce it.