You can close Firefox through the Terminal if it refuses to close through Firefox > Quit
You can open the Terminal by searching for it on the Spotlight (top right corner, magifying glass) Once open, you can run this command to kill the Firefox process: *kill -9 $(ps -x | grep firefox) I’m not a Mac user but that …

How do I close Firefox on Ubuntu?

On Ubuntu, you can force quit the Firefox application by using the pkill command in your terminal. If you don’t already have a terminal window open, you can open one with the CTRL + ALT + T keyboard shortcut.

How do I close Mozilla Firefox?

To close all of the Firefox windows at once on Windows or Linux, click the hamburger button (three horizontal lines) in the upper-right corner of any window. In the menu that appears, select “Exit.” You can also press Ctrl+Shift+Q on your keyboard.