This suggests that Firefox actually is crashing during shutdown. To prevent Firefox from automatically resuming your last session after a crash, you can change a setting.

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the filter box, type or paste resume and pause while the list is filtered

(3) Double-click browser.sessionstore.max_resumed_crashes and set the value to 0. You're done in about:config.

After future crashes, when you restart Firefox, it should present you with a list of the windows and tabs you had open during your previous session so you can choose which, if any, to restore.

It didn't work. I made the changes and closed Firefox. When I reopened it, it said that Firefox was already running, but not responding, so I tried again. Firefox opened with my previous tabs. I then closed Firefox and reopened it. There were no messages about Firefox not responding, but it still came up with my previous tabs.

Make sure that Firefox closes properly and that there isn't a hanging Firefox or plugin-container process left in the task manager.

See:

• "Hang at exit": http://kb.mozillazine.org/Firefox_hangs
• "Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs

Use "Firefox/File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit") to close Firefox if you are currently doing that by clicking the close X on the title bar.

You can also check for error s with session restore.

• http://kb.mozillazine.org/Session_Restore
• https://support.mozilla.org/kb/Session+Restore

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox Profile Folder that store session data.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them).

• http://kb.mozillazine.org/Multiple_profile_files_created

I reset Firefox and it worked.