Rated 5 out of 5 stars

Much better than the built-in Thunderbird alert (which is embarrassingly poor for some reason).

I agree with Qho Li that this needs an option to make the pop-up stay on screen until it is acknowledged either by clicking to open the message or clicking a button to make the pop-up close. That way new messages are not missed if I'm away from the computer.

As far as future nice to have features, it would be nice if it could be configured to show x number of new messages. That way it would display more than just the last message.

This review is for a previous version of the add-on (0.13.4).