Alt plus Ctrl plus delete .it open task manager select processes .then yu can see processes running back ground .sselect Firefox and then click on end process tab

Use "3-bar" menu button > Exit (Power button) (Windows: File > Exit; Mac: Firefox > Quit Firefox; Linux: File > Quit) to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar. In case you use "Clear history when Firefox closes" then try to disable this feature. *https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history See also: *"Hang at exit": http://kb.mozillazine.org/Firefox_hangs *"Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs