Hi,
I don’t know if there is a preferred way to report on Firefox android compatibility with addons not in recommendation program. But here you go.
I can get userscript manager addons (violentmonkey / tampermonkey) work on current Firefox Nightly. But there is a snag that could stump / mislead users.
I have detailed it in a github issue:
https://github.com/mozilla-mobile/fenix/issues/16164