Firefox for android doesn't allow addons and F-droid Fennec doesn't seem to support them either.
The only browser on android that gives me full devtools and addon support is kiwi browser which has it's own skeletons to contend with: https://www.reddit.com/r/uBlockOrigin/comments/ppygw1/can_i_...
- Stock Firefox for Android allows a limited set of extensions including the most popular extension uBlock Origin.
- Firefox Nightly allows the installation of any extensions though this is not enabled by default and requires jumping through some hoops.
- F-Droid Fennec allows the same extension loading functionality as found in Firefox Nightly without having to leave stable.
That said there are still extensions that won't work once installed as not every API is covered. Far more work (orders of magnitude more) than the short list in stock stable Firefox though.
Since I'm not really interested in using nightly or jumping through hoops, I'll just continue using kiwi which is able to support both my requirements just fine.
Thanks for the clarification though.