As you predicted, no answer followed.
For quite a while I used the f-droid-store to install a Version 68 of “Fennec F-Droid”, which you can access by enabling the archive and then scrolling way way down. This has kept me sane albeit vulnerable to security issues.
Now I’ve moved to Kiwi Browser (chromium based) which supports Chrome-Store-Addons. It is faster than the old FF but also getting way too few security updates.
The mobile-browser market has gone down the drain since Mozilla destroyed add-on-support.