Rated 5 out of 5 stars

yazan: Erwane tarih: Ara. 19, 2019 ·

Very nice plugin.
A fork, working on TB 68 is available here :
https://addons.thunderbird.net/fr/thunderbird/addon/new-folder-filters-button/

This review is for a previous version of the add-on (1.4). 

yazan: Chris Malek (Geliştirici) tarih: Ara. 20, 2019 ·

Thank you.
New version "2.0" is currently in a queue for the review.
Once it passes Mozilla review it will be automatically published and available.