uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 57.0.3 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

That is a likely problem caused by a Windows 10 insider update that breaks playing sound in Firefox if you use that Windows version. This should be fixed in the next Windows update. Firefox 58 also has a permanent fix for this.

• https://www.onmsft.com/news/windows-10-insider-build-17063-breaks-audio-in-firefox
• https://www.reddit.com/r/firefox/comments/7kxcf5/latest_windows_insider_build_broke_audio_in
• https://www.reddit.com/r/Windows10/comments/7kzt7s/psa_if_you_use_firefox_dont_upgrade_to_17063_it/

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

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)

from 1426719 comment #38

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

So no workaround patch will be needed in Firefox 52 ESR and 57.0