So, Youtube and other sites work, but with certain embedded video players, clicking the fullscreen button does nothing. The video just remains windowed. This has been a problem for awhile now, and I have been unable to find a solution anywhere, as nobody seems to share my issue. I run Firefox, and have an HP Pavilion laptop. I will upload a screenshot of one of the players that does not work. Also, I tried disabling hardware acceleration and had no luck. RE It is not the website lacking the required code for fullscreen, because this happens on any website running one of these players, and they used to work fine for me.