Recently our HTPC had a video issue and it was resolved by changing the HDMI cable. Oddly, this was the catalyst for a Full screen video issue we now have with Firefox (Edge and Chrome work okay). Whenever full screen video is initiated (Plex, TED Talk, YouTUBE, etc), it initially for about 0.5 a second looks fine, then "zooms in" or crops the image so that that we only see the upper left portion of the video in full screen. I have tried replacing the Amplifier (before I realized it was only firefox), reinstalling Firefox, updating our video drivers, and have completely replaced all HDMI cables. Please, if someone could offer a suggestion. I can't figure out what's going on here.