What's the status of this project? Is there a project page?
You're looking at it! This gives an overview of known open work:
If you look a lot of this is "internal" IT stuff and also many bugs we found on the Big Sur betas - some of which might have been resolved already in the final release. There's still a bunch of programming work outstanding for features that we could disable, or external tools, for example: https://bugzilla.mozilla.org/show_bug.cgi?id=1650612
We just put the first Nightlies out today, so I think that as people start using it and we find any Apple Silicon specific bugs the list will start growing again. The main limitation is hardware at this point. We only have a few machines.