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.
