About two week ago my Firefox audio was playing but very low or no sound at all. This was happening on anything with video (Youtube, local news sites, etc.). When I would bring up the sound settings I would see a separate audio slider for Firefox and it was set to either very low or off. If you slide the slide up, Firefox would play sound just fine, until you closed it, then, on the next opening of Firefox the volume would be very low again.
After a few google searches of this problem I found a solution that worked for me.
1. Open a Terminal Window.
2. In the Terminal type the following and hit ENTER
rm ~/.config/pulse/*
That's it. You should now have your sound back in Firefox. Since this fix remove files involved in PULSE AUDIO (your sound system files) other programs may have the same issues and not just Firefox. I had about six files in the ~/.config/pulse/ directory, all of which looked like temp files and one was called cookie. So if you're having trouble with sound in a app this may fix that too, not just Firefox.
NOTE: My Firefox version is 102.0 (64-bit).
