Just to be clear, which firefish server did you join?

I just checked out the main server (firefish.social) and there wasn’t any transphobic content in the “Global” or “Local” section.

I’m wondering if you ended up on a really toxic right-wing fediverse instance, that happens to use Firefish as its software, and so the Firefish main site stupidly/ignorantly listed it as a possible place to sign up. If that’s the case they need to get rid of it.