Cool New Firefox Feature

Firefox somehow broke my ability to access my torrent client's web client? When I try to access it in firefox, I get an "Unable to Connect to Client" message. It doesn't work if I use that computer's network name or if I use its IP address. Both work fine in Safari and using curl. It also gives the same error if I try to access my nginx server over HTTP (I haven't confirm if HTTPS works with those addresses because I don't want to go through the hassle of setting up a self-signed certificate).

I thought it was that Firefox has blocked HTTP or something but I have 'https-only' mode turned off in the settings and also I can connect to my router via http.

Now, I can hear you already:

The new version of macOS makes access to devices on a local network a permission you need to grant.

I'm aware. I already had given Firefox access for this specific use case. It worked until I updated Firefox. I tried turning that permission off and on again in case it was somehow causing it but Firefox actually gives a completely different error when the setting is off ("Hmm. We’re having trouble finding that site.").

Anyway, if you know how I can fix this I guess let me know.

EDIT: What the hell it works again as of this morning. I did not do anything to either computer between now and then. Neither computer was restarted. Firefox has remained open