Rated 4 out of 5 stars

Will this useful extension work with Thunderbird 3.* in future?

This review is for a previous version of the add-on (0.3). 

Yes, as said in the extension's description, the 0.3 version of Display Quota has been ready and is just awaiting mozilla's reviewers' validation since october the 8th... I really hope they will review it and allow it to be published soon...