That's a shame, I would have loved to keep using those thorns and eths. Quite weird to think that they didn't even want to ask for a few customs pieces for those letters.
Found a solution, thanks to Bigsleep62:
"I solved this problem by going to settings -> system -> sound, then under "Advanced" click "Volume Mixer," then at the bottom press "Reset sound devices..." Windows 10"
It worked for me on Windows 11 too
Firefox 131.0.3 has no sound and it does now show up on volume mixer
Did anyone else have any problems? It was working fine yesterday, but now it isn't, so I'm not sure if it is related to this version
Firefox Nightly 132.0b8 is working fine
edit: I should mention that I already restarted win11, restarted Firefox, tried under Firefox safe mode with extensions disable, but the problem persists