HI, see if anything here helps : VIDEO AUDIO

• https://support.google.com/youtube/topic/3014746 - Youtube
• https://www.youtube.com/html5/ - Can you support HTML5
• https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues
• https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox
• https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows

if not : SAFE MODE

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

In Firefox Safe mode these changes are effective:

• all extensions are disabled (about:addons)
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored (chrome folder)
• default toolbar layout is used (file: localstore-safe.rdf)
• Javascript JIT compilers are disabled (prefs: javascript.options.*jit)
• hardware acceleration is disabled (Options > Advanced > General)
• plugins are not affected
• preferences are not affected

TEST''''is issue still there ?

If above Support Documents do not help and the issue is still there after Safe Mode please : uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData 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 61.0.2 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.

After following above, the video still plays but without the sound.

Did you check your Audio speaker to make sure it was set to the right speaker output?

I have a Bose surround sound system and the TV is set-up to Audio System. watching the TV channel is working. Audio when I watched video (You Tube, Pandora...etc.) directly from the TV, it is working. The audio doesn't work only when I am watching videos on Facebook, you tube...etc from the computer with the Firefox browser. I wanted to find out if what the flash player that Firefox browser uses is compatible with the Sony Bravia XBR-65X850B that i have or do I need to install a different flash player? I think it first started when Firefox did an auto-update on my computer. Before, I will just try to update the Adobe Flash Player and it will work again. I tried updating Adobe Flash Player and but now it doesn't do the trick anymore.