Since done the reinstall stuff might as well : 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 57.0.2 with a Full Version Installer *https://www.mozilla.org/firefox/all/ If still issues : Create a new profile as a test to check if your current profile is causing the problem. See "Creating a profile": *https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem. Never work with original files. *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox Please let us know if this solved your issue or if need further assistance.

That is a known problem caused by a Windows 10 update that breaks playing sound in Firefox. *https://www.onmsft.com/news/windows-10-insider-build-17063-breaks-audio-in-firefox *http://forums.mozillazine.org/viewtopic.php?f=38&t=3036696 *[https://bugzilla.mozilla.org/show_bug.cgi?id=1426719 bug 1426719] - Latest insider build of Windows 10 (17063) breaks sound playback completely (<i>please do not comment in bug reports<br>https://bugzilla.mozilla.org/page.cgi?id=etiquette.html</i>)

''cor-el [[#answer-1054000|said]]'' <blockquote> That is a known problem caused by a Windows 10 update that breaks playing sound in Firefox. *https://www.onmsft.com/news/windows-10-insider-build-17063-breaks-audio-in-firefox *http://forums.mozillazine.org/viewtopic.php?f=38&t=3036696 *[https://bugzilla.mozilla.org/show_bug.cgi?id=1426719 bug 1426719] - Latest insider build of Windows 10 (17063) breaks sound playback completely (<i>please do not comment in bug reports<br>https://bugzilla.mozilla.org/page.cgi?id=etiquette.html</i>) </blockquote> Thanks, looks like there is nothing I can do for now, will just use edge "for YouTube" until this is fixed.