sound not working on YouTube
there is no sound whatsoever when using YouTube, that is on YouTube itself. The problem does not exist if I use the Google browser
Youtube currently uses the HTML5 player.
While a video is playing, does Firefox display a little "speaker" icon on the tab (assuming you are not in full screen)? If Firefox does NOT display the icon, there may be a problem decoding the audio out of the video.
If Firefox displays the audio icon, does clicking it make any difference? It operates as a mute/unmute button.
If Firefox thinks it is sending audio to Windows, could you check the mixer? On the Windows Taskbar, in the "notification area" at the lower right (sometimes called the system tray), right-click the speaker icon and choose Open Volume Mixer. Here you can see whether Firefox shows any volume or is muted at the system level. Anything unusual?