Anything like that for Firefox Android and the extensions that Mozilla didn't whitelist? I followed their procedure for Nightly with a custom add-on collection but it didn't work.
https://blog.mozilla.org/addons/2020/09/29/expanded-extensio...
https://blog.mozilla.org/addons/2020/09/29/expanded-extensio...
https://f-droid.org/en/packages/us.spotco.fennec_dos/
But Nightly also works with add-on collections for me. Which step are you stuck on?
Here is mine : https://addons.mozilla.org/fr/firefox/collections/17173754/t...
If it helps, the biggest issue I had with setting up custom extensions on Firefox Nightly Android using spaces in the collection name.