Web page displays like this (Video Thumbnails in a column on the left side of the frame) and asks for a player app when clicking on thumbnails. YouTube videos play perfectly on FaceBook and other pages however when I click on play in YouTube the page displays as described. This is not a problem in other browsers. I have gone back in Time Machine and also downloaded a brand new FireFox browser. I have also tried trashing secondary FireFox files all to no avail. Presently I can't even upload a screen capture of the problem.