In the last few months Firefox behaves badly when playing Youtube and Vimeo videos. Sometimes it freezes; sometimes the aspect ratio of the video gets badly-stretched or the video takes over the entire window that Youtube or Vimeo is running in. Sometimes the Youtube or Vimeo player is missing a control such as the volume control or icon to "like" the video, etc. If I copy and paste the URL from Firefox into Chrome, there are no problems at all. If I use Chrome exclusively to visit those websites there are no problems. This is strictly a Firefox problem. I have many other video-playing apps on my PC such as Adobe Premiere Pro, VLC, Windows Media Player, etc, and none of them are having problems. I've done several updates of Firefox with no relief.