Rated 5 out of 5 stars

This is a fantastic add-on, but now the folders are lost whenever I restart Thunderbird. I'm using TB 3.1.15 with QuickFolders 2.9

This review is for a previous version of the add-on (2.9). 

... please go here:

http://quickfolders.mozdev.org/bugs.html

And yes, this bug is already fixed - Simply install QuickFolders 2.9.1 <:o)

https://www.mozdev.org/bugs/show_bug.cgi?id=24461

The bug only affects TB 3.0 and older - remember, the current release version of Thunderbird is 7.0.1