princefabrizio.wixsite.com/inventions:
You are using Linux. If you are using alsa instead of pulseaudio this
behavior is expected. Support for alsa was abandoned by Mozilla. My SM
is also affected.
A workaround for SM is using apulse. This gives sound in the browser.
But sadly not in the cases you mentioned. Some time ago I tested TB to
be sure not only SM was affected and filed a bug against apulse:
https://bugs.gentoo.org/691982
Not much traffic in this bug. *g* Well, I missed the notification of new
mail by sound enough that I tried another way. With success. Works not
only for my SM but also for TB. At least for an old Daily.
I installed pulseaudion on top of alsa. For this I had to get rid of
apulse and also some tweaks were necessary.
Hartmut