sound not working

Sound is not working (system volume not muted as well as lichess volume). Using Linux

This happens occasionally. I wish I knew why.

I have the same problem. Firefox 38.0 - elementary os 0.3

I see these reports from time to time. Everyone seems to have firefox on linux.

If you use pulseaudio, check that sound isn't turned down in pavucontrol for that application. Mine was down to 55% randomly

You can also see if it resolves by restarting pulseaudio, which also requires restarting firefox. Other applications might hang or crash when doing this, recommend to close them all.

pulseaudio -k && pulseaudio --start

Same here, sometimes I don't hear sounds (but I can hear other sounds on my computer fine). Firefox 38.0.5 on Windows 7.

Seems like pretty common issue. Given your answers, I started to use chrome for lichess, where the sound works fine so far..

Yes, sometimes the sound begins to crack, pulseaudio starts using the CPU at 100 percent.
And this helps only:
>pulseaudio -k && pulseaudio --start

http://le.lichess.org/forum/lichess-feedback/lichess-kills-sound-on-computer?page=6#60