Two thumbs up dev(s), hope you're doing okay and getting some sleep in between. Had some rough production upgrades in my life, and this sounds like a pretty bad one. 😖
Firefish definitely seems like it's overly concerned with aesthetics over anything else. Nearly every instance I checked out had a ton of custom CSS which frankly reminded me more of something like Tumblr than what it really is (Mastodon with a coat of paint.) I don't mean this as a slight since it's obviously attracting a community, but it's completely inscrutable to users not familiar with the platform its based on and seems to be very taxing to maintain (my experience mirrors yours somewhat.)
If they can get more people on board to keep it together then I'd definitely be willing to spin up another instance.