If the sound disappears from browsers etc. and you get something like:
ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave Playback open error: -16,Device or resource busy
try to find and kill pulseaudio processes:
lsof|grep snd ... pulseaudi 18515 pink mem CHR 116,3 4059 /dev/snd/pcmC0D0p ... kill 18515
and restart browsers.