How to enter/exit full screen mode in FireFox?

Suddenly, I enter the full screen mode of firefox. I do not know which key I pressed to enter the full screen mode. I press Esc to try to exit the full screen mode but it does not work. I move mouse pointer to the top border of screen, then the menu bar appears but when I move the mouse pointer away, it enters the full screen mode again. It seems the mouse pointer can only disable the full screen mode temporarily. How can I disable the full screen mode permanently? In fact, you can press the F11 key to exit the full-screen mode. The F11 key is also the key to enable full-screen mode, i.e., you press the F11 key to enter the full screen mode and press F11 again to leave the full screen mode. The F11 key is the switch key. The reason I entered the full screen mode unconsciously is that when I tried to type the backspace key, I actually typed the F11 key by mistake.

This is the design defect of Firefox. It should use the Esc key as the key to exit the full screen mode as most other apps do.

 

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