By default, reinstalling or installing beta versions will not help, as most issues are related to settings in your profile, i.e. the user settings.

Could you take a look at the What to do if Firefox won't play any sounds support article to see if anything there (or referred to) helps? Please let us know if it did not.

Tuishimi said

... on Windows Insider Preview 171213-1610 What more can I provide you to help troubleshoot this issue?

This was due to you using the Insider Preview builds and not due to a Firefox update.

https://www.onmsft.com/news/windows-10-insider-build-17063-breaks-audio-in-firefox http://forums.mozillazine.org/viewtopic.php?f=38&t=3036696

Mozilla does have a patch on recent Firefox Nightly builds but is this really the best option when the Windows update was the cause.

I chose to close this since the developers know what the issue is and one way or another, it will be addressed in the future.

Downloaded nightly and it is fixed.