Rated 1 out of 5 stars

Used this plugin for a couple of years and then it stopped loading conversations when Thunderbird was restarted. Many have this problem and it was never fixed. I would not recommend it as there are other existing problems. And it appears the plugin is not going to get any serious support.
The only solution is use TB's built in conversation mode. It's not bad. The plugin helped streamline it but you have to use what works and the plugin doesn't.

Stay away from Mailbird. I allowed myself to be sold on it and what a waste of money. I bought strictly to be able to use a better conversation mode since this plugin started failing but organizationally Mailbird was written by 12 year olds. It is not an email app for real business users. It lacks so many features it is laughable. And will not import IMAP accounts. This is a fair warning, you will regret it if you purchase.

Thunderbird is still the best email app around.

This review is for a previous version of the add-on (2.11.4).