Good, but better alternative exists Rated 3 out of 5 stars

This add-on ( ver. 0.6) is working fine for me in TB 3.1.7

But there is a better implementation with extension "Manually sort folders" (ver. 0.6.6)
1. Allows for sorting of folders, not just accounts
2. Has same sorting options, but more sort methods
3. Easy to get to sorting in the Tools menu
4. Better GUI, both in look and function

I tried both, and for now "Manually Sort Folders" just does it better
https://addons.mozilla.org/en-US/thunderbird/addon/15102/

This review is for a previous version of the add-on (0.6).