''I have been experiencing this weird problem since I updated my Mac from Catalina to Big Sur. On full screen mode, the menu bar is normally hidden and whenever I hover the mouse pointer at the top, the menu bar automatically becomes visible. Sometimes, without any pattern, the menu bar stays there even I hover the mouse pointer the bottom or somewhere. To solve this, I always need to quit and full screen mode. As far as I know, this happens only in Firefox. Is there anyone having such an issue (and a solution for this)?'' I have the same problem. It's really very annoying. Any suggestions? https://www.reddit.com/r/firefox/comments/ko9us5/randomly_stuck_menu_bar_on_full_screen_mode_in/ https://www.reddit.com/r/firefox/comments/kxilb7/macos_big_sur_firefox_fullscreen_rare_annoying/