Are you using Windows 10 Insider builds?

If so the sound likely still works in anything using the Flash Player Plugin from Adobe in Firefox but not in HTML5 player.

Mozilla has a working workaround patch in upcoming Firefox 58.0 (Jan 23) and maybe for the Firefox 52 ESR as Microsoft may be a while fixing this on their end even with the cause known.

Bug 1426719 -Latest insider build of Windows 10 (17063) breaks sound playback completely Bug 1426285 - HTML5 no sound/audio

Hmm so it appears the next Win10 Insider update (when it happens, in March?) will have this issue fixed.

Thanks for the response. Yes I am using Windows Insider build. Hopefully issue will be resolved in 58.0

See also #1426719 (FIXED in Firefox 58):

• bug 1426719#c35 - Latest insider build of Windows 10 (17063) breaks sound playback completely

I am using below Nightly build.

I am using below Windows build.

Sorry no help. Use release version. Wait for Windows to fix issues. There are too many variables to trying to fix a Firefox Beta and a Windows Pr-release build.

This should have been fixed in Nightly about two weeks ago and on Beta a week later.

• https://hg.mozilla.org/mozilla-central/rev/6217d397dc08
• https://hg.mozilla.org/releases/mozilla-beta/rev/cb9a0bfe28ea476c6299d7684dab4b6f2a0b4e0f

Pkshadow said

Sorry no help. Use release version. Wait for Windows to fix issues. There are too many variables to trying to fix a Firefox Beta and a Windows Pr-release build.

The audio issue on HTML5 player video is due to recent Win10 Insider builds, not due to any version of Firefox. As cor-el said a workaround patch has been on Firefox Nightly channel for a couple weeks now.

from 1426719 comment #38

Heads-up, Windows fix has reached mainline as of build 17073

So no workaround fix is needed in Firefox 52 ESR and 57.0