I think your comment is also making plenty assumptions..

Official Firefox can be leaky unless you build it yourself with some build-time changes or use a fork with such[0]. Am I guessing right that you still have Webcompat, RemoteSettings, and Nimbus enabled still? How do you know a compatibility intervention isn't causing your browser to open the kimono just enough to "unbreak the page"?

> My guess is that OP's browser is getting banned because his WebKitGTK has a weird fingerprint, not because of webgl or whatever.

My guess is a different flavor of the same: Not matching an expected fingerprint (simplified: whitelist vs blacklist approach) combined with other factors.

[0]: I'm currently aware of Tor Browser, Konform Browser (am dev), Mullvad Browser, and to a certain extent Waterfox, LibreWolf, and r3df0x doing that.