Did you update from an older version?
I remember at one recent version change Mozilla decided to "require" pulseaudio - and so apulse was born, to fake it, sort of.
IIRC apulse was originally conceived to fix skype audio but now adapted to firefox.
]]>Later on, I found that I have no sound in Firefox. So, I'm guessing that YT did some thing to FF.
Any ideas how to solve this issue?
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