I just checked and when my videos are in full screen mode, there is no way to pop down the red/amber/green buttons. I tried putting my cursor up to the top but nothing happened. I wasn't stuck in full screen mode I was just checking to see if I could see the buttons. Nope. Not while in full screen mode.
The keyboard shortcut for exiting full screen mode is to hit the ESC key.....did that not work for you?
The other method for exiting full screen mode is to push your cursor off the top of the screen to reveal (pop down) the normal red / amber / green pills, then click on the green pill to toggle out of full screen mode and return to standard window display.....did that method quit working for you?