peeking in .......................
another puzzle for atty

i went to about:config and looked for browser.fullscreen.autohide and it was set to false. btw that was user set. i remember finding a list of recommended changes when i first switched to ff. so what happened?
IDK what version you are running. However, there are a few keystrokes that can invoke it and also there's a button on some of the menu bars that starts it. F11 will toggle it.
Now, some laptops have FN-Keys on the keypad too that are accessed with a special key held down. And if it's a touch screen, you could have hit the buttons on the menu bar while pressing the screen.
Who knows? You can (with my current version, anyway) get the menu back by moving the cursor all the way to the top edge of the screen...the menu slides down back into view. From there you can "un-click" the full-screen button (looks kind of like a plus sign with a screen in the middle)