Ok, I?ve had more time to think about it, your issue reminds me of my issues with multi-channel audio on alsa like a decade ago in my early (earliest really) days of using linux. Basically getting no sound except when running an audio test.
What I believe could be happening is that the audio test is a multi-channel track that fires off on all available channels, while the firefox audio is just stereo and it could be firing off on any of your channels, so for instance maybe it’s going off in the subwoofer and is therefore poorly audible.
There’s a few things worth trying in no particular order.
Try opening alsamixer (in a terminal) and messing with the settings in there, remember to press f6 to select an audio device. In there you can mute and adjust volume for specific channels, it could be that whichever channel you need is just muted or set to 0 volume.
I found this when searching for multi-channel pipewire guides:
Might be worth reading through.
This here
Settings
└─ Default Configured Devices:
0. Audio/Sink alsa_output.pci-0000_26_00.1.pro-output-3
I believe could be a hint, that’s the alsa identifier for the default output device and it say output 3 implying there might be 2 others, I’m not entirely sure how to change these (I would’ve figured alternatives would be listed under sinks)
But you could try disabling pipewire and seeing how your audio behaves on alsa alone.
Could also try swapping pipewire out for pulseaudio, but I really do not recommend that as a long term solution even if it works because pulseaudio is bad. But it’s acceptable if you are happy with the results, the biggest issue from an end user perspective would be the high latency.