Rated 5 out of 5 stars

This is an incredibly useful add-on. If you use Thunderbird professionally and have a well structured directory/subdirectory organization for your thousands of emails, you need a way to get to the 3 or 4 main directories that you access most frequently. This Add-on provides that functionality. I tested it for 5 minutes and gave them the $15 fee for Pro version as a donation. To the creators of QuickFolders--- great add-on, thanks for doing this work.

This review is for a previous version of the add-on (4.14.1). 

Thanks - if you are looking into future proofing for next years version of Thunderbird (ESR 68, due to come out after July) you can check out my conversion efforts (and download trials) here:
https://www.mozdev.org/bugs/show_bug.cgi?id=26658

Note that b/c of technical reasons, the new version is not compatible with the current Thunderbird version (60) - functionality will be the same, as much as possible and pending on any future restrictions coming down the pipeline from Mozilla.