I'm afraid I don't have any real solution, since I get Firefox from the play store, but its my secondary browser; I get Mull from Obtainium (kinda like a Librewolf for android), you might look into that? I know this is kind of not what you wanted to hear though and im sorry
Are you sure the GitHub releases aren't being updated anymore? When I checked here not too long ago, they were still being updated. I know they said they changed the positaries, but I don't know how long ago that was. But I know for a fact that I was able to pull Firefox focus version 122 off of GitHub.
Fennec 127 on fdroid. Now that I think about it, I believe I did see a post the other day about Mozilla completing a move to some other system. Let me see if I can find it.
Edit: Here it is, though I'm not sure if this will help at all. But it may at least explain something.
Not really. Safest place to get an app is from the Dev if you're not using the play store. FDroid has been known to host out of date packages forever, causing security concerns.