Ok, looks like the onion address worked on my graphene phone too, so thats good. Thanks!
You would need to download and trust your servers Root Certificate Authority (Root CA) on every device you want to connect to your Start9 server. I have a similar setup like you and that's what I did. To connect remotely to your Start9 server you would need the Tor browser and the .onion address you find under Settings --> About
I also found this instruction which might help with your Librewolf's issue if you haven't tried it:
https://docs.start9.com/0.3.5.x/misc-guides/ca-ff#ca-ff
Hope this helps.
Discussion
You're very welcome. Have fun with your new Start9 server.