Malazan said

I stopped being able to hear audio on Youtube videos about 30 minutes ago. With the videos I had already clicked into before the issue occurred, I could still hear these video's audio - then I closed these tabs. Closed the browser. Restart the computer. That didn't work. Tried using safe mode and clicked into a Youtube video, still no audio. But audio works perfectly when I uses Google Chrome.

Updated: I updated the three Plug-Ins: Flashplayer, VLC player, and the pdf one and restarted Firefox and the problem still isn't fixed.

Did you check the volume in the Windows Volume mixer for Firefox and for the Flash plugin (plugin-container)?

Does it make a difference whether you use the HTML5 media player or the default (Flash based) player?

• http://www.youtube.com/html5

See also:

• https://support.mozilla.org/kb/fix-common-audio-and-video-issues