Great, great add-on, but does not work with latest beta (50) Rated 5 out of 5 stars

I missed this so much, I reverted to TB45

This review is for a previous version of the add-on (4.5). 

Thunderbird 50 compatibility is coming...

... there is already a bug fixed beta version here:
https://www.mozdev.org/bugs/show_bug.cgi?id=26224
I recommend waiting for the official release of QuickFolders 4.6 - we are just in the process of moving the web site, and will release once that's complete!