Firefox (sound cuts out randomly)?

Question

Browsers

The latest version is 58.0.2 (64-bit). Other audio playback devices work fine. The first time, it happened about a week ago, the sound disappeared on all sites, the videos themselves are played normally. It went away on its own after a few browser restarts. Some time later, it happened again. In the volume mixer, the volume slider is set normally for the browser. Didn't install any plugins. I just watched streams on twitch, and the sound itself disappeared. I repeat, and disappeared on all sites. The icons on the tab for turning on / off the sound are also missing.
upd.
The problem affected all browsers in general, including Chrome, as well as Firefox version 56, for which a separate profile has been created and there are no third-party plugins and even tabs at all, it is essentially clean.
upd. 2
There was some kind of global problem in Windows itself, I decided in Media Player Classic to start the movie and there was no sound either, I started randomly rewinding to different places in the movie and the sound was restored. Immediately launched the browser and there the sound was also restored. At the same time, the song played in AIMP all the time, that is, any physical problems with the speakers, cable waste, and the like, are excluded.
I would like to know the reason in order to prevent the occurrence of this. Windows 7 64-bit system, no other problems or errors were observed. I have not installed any software during this time.
Well, I’ll add the last thing, the sound slider in Windows did not give a characteristic sound when you click on it, while I repeat, all the time the problem arose, through AIMP, the song was playing, extremely strange.

Answer 1

Control panel - sound - playback, check that you have the correct playback device selected, perhaps for some reason you have a randomly different device appearing there, which was once selected as 'default', just select any other device and back to the desired one.
Players like aimp can independently remember the selected device (media player classic too, but default is default)

Answer 2

I have the same problem now. And randomly occurs