Is it the screen that says "This is embarrassing..."? That page displays if Firefox crashed during shutdown and either is not set to restore automatically after a crash, or automatic restoration already failed at least once.

So... that raises the question of whether there is some reason Firefox would be crashing during shutdown. That "crash" could be anything that prematurely terminates Firefox's file maintenance tasks that it performs at shutdown, such as Windows killing the process.

I don't know what's causing this seeming shutdown crash, but that's what I think we need to investigate.

How do you close Firefox? There's a better chance that everything will get taken care of if you use the menu rather than the "red X" button:

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

Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

You can check for problems with the sessionstore.js file in the profile folder that stores session data. When sessionstore.js is deleted you lose pinned tabs and Tab Groups and open tabs and you will have to recreate them, so if necessary make a note or bookmark them.

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

I'll try shutting down with the file menu instead of the red x, and see if that helps. If not, I'll try the next suggestion. Thanks.

jscher2000, thanks. Your solution did the trick. Much obliged.