You can check if you have a user.js file in the Firefox profile folder that sets the browser.sessionstore.resume_session_once pref to true.

• http://kb.mozillazine.org/browser.sessionstore.resume_session_once

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

It is possible that Firefox doesn't close properly. Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

See also:

• "Firefox hangs when you quit it": https://support.mozilla.org/en-US/kb/Firefox+hangs

I redid all of the fixes and it's working properly.

Thank you, John

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily. Thank you for contacting Mozilla Support.

Problem is back and this comes up again.

Well, this is embarrassing.

Firefox is having trouble recovering your windows and tabs. This is usually caused by a recently opened web page.

You can try:

   Removing one or more tabs that you think may be causing the problem
   Starting an entirely new browsing session

Hi johnarg, do you use CCleaner? If so:

Can you go into its settings and deselect the option to clear your Firefox session data? Firefox 56 changed the format and name of the session history files, and this seems to have created a temporary compatibility issue with the cleaning feature that somehow is causing this problem.

Thank you! I am using CCleaner and I have just unchecked the session box. We'll see what happens.

Thanks again, John