Can you disable that popup after you enter full screen ? I know you can tick the check box to not show this again, but is there anyway to prevent it at all ? These little things, all add up..... Whats maybe more important is, why is popup there at all ? People can obviously see there in full screen mode, and they should already know the key combination to exit full screen mode.... That's what the documentation is for.
There's a small checkbox at the left bottom of that message, "don't show this again". When you check that you won't be shown that message again. Granted, the usability of that function could be improved as you don't immediately see the checkbox.
