That sounds like a message from Windows. Not Firefox. Have you noticed any problems of late? Start '''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Firefox in Safe Mode]''' {web Link} by holding down the '''<Shift><br> ''(Mac Options)'' ''' key, and then starting Firefox. Is the problem still there?

Sounds that Firefox is hanging. *"Hang at exit": http://kb.mozillazine.org/Firefox_hangs *"Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs You can try to disable hardware acceleration in Firefox. *Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available" You need to close and restart Firefox after toggling this setting. *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes You can check if there is an update for your graphics display driver and check for hardware acceleration related issues. *https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration ---- If you have submitted crash reports then please post the IDs of one or more recent crash reports that have a "bp-" prefix: *bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx You can find the report ID of recent crash reports on the "Help > Troubleshooting Information" page (about:support). *Click the "All Crash Reports" button on this page to open the <b>about:crashes</b> page and see all crash reports. If necessary then you can open <b>about:</b> pages via the location/address bar. See: *http://kb.mozillazine.org/Mozilla_Crash_Reporter *https://support.mozilla.org/kb/Mozilla+Crash+Reporter