I just had Windows 10 installed (Windows 10 - pro 64 bit) Naturally i installed Firefox as the first as its my preferred browser. However I can play youtube videos just fine. But when i want to play fullscreen it tells me my browser isnt supporting fullscreen. The link it provides tells me to check about:permissions and look for something named "fullscreen" settings for the particular site (which in this case is youtube.com) However there is no such thing about fullscreen. I have things like permissions for the site using my microphone, showing popups and using my location. But nothing about full screen. If i have firefox forget settings for youtube.com it will work fine. Untill next time i want to play a youtube and I have to forget that site once again. What am I missing here ? I appear to be using the latest firefox as its fully updated.