Try using Exit on the menu. Either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

Pause 10-15 seconds while Firefox finishes its cleanup before having the Flash installer proceed.

Does that work any better?

Worked like a champ. Thanks. I've saved your reply for the future. Thanks again.

This doesn't help me because my problem occurs virtually every time I shut my computer down. The next time I boot up my computer and hit the firefox icon, I get a message about session restore. Why can't Firefox just shut down when I hit the x in the upper right corner before I power down my computer

Hi mark7432, Firefox performs various file maintenance tasks at shutdown. If that process is not completed, Firefox may behave as though it crashed. While we all would prefer that Windows were patient enough to wait, as you can see, it often "kills" Firefox prematurely if you rely on Windows to shut down running applications.

I appreciate your answer, but it really does not give me a solution. Is there anything that I can do to control the problem. I have tried waiting 10-15 seconds before powering off my computer, but the results are hit and miss. Do you suggest that I wait a longer time before I power off my machine? and if so, how long? Thanks for the help

Hi mark7432, 15 seconds would normally be enough on a fast system.

If you want to check how long Firefox is taking to fully exit, and you run Windows, you can use the Windows Task Manager (Ctrl+Shift+Esc). On Windows XP, Vista, and 7, click the Processes tab and look for firefox.exe there. On Windows 8, 8.1, and 10, click the Details tab if Firefox is not on Processes. Similar features may be available on Mac and Linux.

Some users have reported that Firefox 44 is taking an unusually long to shut down or "hangs" during shut on their system. This may be invisible or Firefox may display a crash report dialog after some period of time, as long as 5 minutes. I have not yet seen an explanation for that issue on those systems so I don't know how to check whether you are having that particular issue.

mark7432 said

This doesn't help me because my problem occurs virtually every time I shut my computer down. The next time I boot up my computer and hit the firefox icon, I get a message about session restore. Why can't Firefox just shut down when I hit the x in the upper right corner before I power down my computer

The X on Firefox window only closes that one window and not the whole Firefox unless that was the only Window open.