I am not sure if this has anything to do with your problem, but maybe
check also for this:
Using KDE Plasma and knowing that PulseAudio is in use, I am observing
since roughly 3 months now that for unknown reason Firefox started to
kind of randomly appear configured with the application specific audio
volume set to 0%. I have no idea why sometimes Firefox starts up at 100%
volume as it should be, and sometimes at 0% as it (for me) should not
be. I for now suspect, that there is some application audio volume mixer
in PulseAudio active, and this mixer supposedly stores for each
application an individual volume level before it streams a final audio
stream to the audio card which then has its global volume adjustment
available. Unfortunately, Firefox becomes (sometimes) configured in the
supposedly present mixer with the (by me) unwanted value of 0%.
At least I have my workaround for it:
This setting appears in KDE under: System Settings - Hardware - Audio,
there on the Tab "Applications", where "Firefox: AudioStream" appears
with its individual to the application configured value, as soon as
audio is to be reproduced by this application (currently audio inactive
applications are not shown there). It consequently can be readjusted to
the wanted value. The same configuration option is also accessible via
the audio icon in the System Tray, and from there faster to reach.
Maybe you experience something similar and haven't been aware about this
application specific setting to exist, and like it unfortunately happens
sometimes to me maybe also for you Firefox there is now set to 0% ?
Good Luck! Marco.
