Hey @nalexander, thanks for reaching out! It’s great to see Mozilla integrating with community projects like Tor and F-Droid! 
The only make or break thing is proprietary software. As far as I remember, that’s only the Google Play Services GMS libs used for Chromecast. We will include anything that is 100% free software that can be built from source on our builders. Certain things are allowed, but will be marked with an “Anti-Feature”, like if the app tracks the user. Firefox Klar is not marked this way since the tracking is opt-in.
So features that require a proprietary network service can be included, but will be marked with an Anti-Feature. If it is a free software network service, then it would not receive any Anti-Features.
We’ve also done a lot of work on making reproducible builds a lot easier. We have an optional workflow where an APK can be accepted with the developer’s APK signature rather than the f-droid.org signature, as long as f-droid.org can reproduce the APK from source. This is working now, but it is finicky and not easy. We’re starting to work with Tor Project on getting Orfox and Orbot working via this process.