From Thunderbird 60.x, due to major changes made in Firefox by Mozilla, many patches are needed in Thunderbird Addons, just to be compatible with new Thunderbird versions, without adding any new features (see https://wiki.mozilla.org/Thunderbird/Add-ons_Guide_57).
Also, the future architecture of Thunderbird is currently being discussed, with the goal to make its development autonomous from Mozilla. At the moment it’s not clear how this will impact Addons.
For these reasons, since I haven’t got enough time to put in it, I’ve suspended the development of my addons.
This was not an easy decision to make, after all those years.
All the source code is available on GitHub, for anyone who wants to help.
I want to thank everyone who helped and supported me.