Developer reply by Alexey Bazhin
Rated 5 out of 5 stars
Unfortunately no longer usable in the current version.
:-(
Thunderbird Version: 60.9.1 (old Version)
What is the "current" version?
It is targeted to latest stable version 78 and up.
Versions below covered with original addon.
To create your own collections, you must have a Mozilla Add-ons account.