I made something like this before, but i found something interesting. Ever since I installed the new Firefox beta's, initially from Firefox 28.0(which was working fine), these problems occurred. I also have no sound, whatsoever on any site with Firefox. Even If i uninstalled and went back to 28.0, the problems follow me there too. Basically, when I click on a youtube video and monitor the quality, it goes from 360p to 240, then from 240p to 480p, and then 720p, then 1080p, eventually the video crashes inbetween then from such rapid switches. I have youtube set as 'never run in automatic high quality'. My flash player is the latest, my java is the latest, I ran a malware scan and came clean, I ran both chkdsk /r and /f today. I uninstalled about x5 times, still same result. If i used the HTML5 player, every video would have only 360p quality available. The first 10-20 seconds would lag a lot, the buffer symbol would appear every approx 2-3sec. but eventually the video plays normally, still with no sound.