I'm wondering.. Would you use Tor Browser for self-hosted or friendhosted onion services? Or would you use your own Firefox+socks proxy specifically for these services?
I reckon there might be a lot of ways for Firefox to leak which addresses you visit. Especially default incl. telemetry and depending on extensions installed and your personal profile settings, many of whom probably could be limited by using privacy-enhancement such as https://github.com/arkenfox
But if you or friends own the servers in question, don't visit other onion sites from that browser, and you don't really care about the history of visited sites on your FDE PC would you really gain anything by using Tor Browser? Fingerprinting has a lot to do with host of the onion service, right?