How to disable this message: "YouTube.com is now fullscreen. Press Esc at any time to exit" Open a new tab. Enter the following in the address bar: about:config Enter the following in the filter box: full-screen-api.approval-required Double-click to set the parameter to false - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - How does this message help anyone? If this is a security feature, the idea is to prevent an un-authorized fullscreen mode. I clicked to make it full screen!