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

Your System Details list shows that you have a user.js file in the profile folder to initialize prefs each time Firefox starts. The user.js file will only be present if you or other software has created this file and normally won't be present.

You can check its content with a text editor (right-click: "Open with"; do not double-click). The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session.

You can delete the user.js file if you didn't create this file yourself.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Thank you for the speedy response! I deleted the user.js file, but it was recreated when firefox opened. I will try the other ways of exiting and see if they work.

You may have corrupt sessionstore [v56] sessionstore.jsonlz4 file(s). Delete all sessionstore* files and the sessionstore-backups folder.

Type about:support<enter> in the address bar.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder

Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.

Locate the above file. Then rename or delete it. Restart Firefox.

Don't delete the files if you need to rescue any data from them, just move them out of the profile folder to some location where Firefox doesn't look for them. You can try to read out their contents using this tool: https://www.jeffersonscher.com/res/scrounger.html

I'm afraid this did not work either. I moved both the folder and the sessionstore file to my desktop and Firefox just makes another folder and restores from that instead. The sessionstore file has not been recreated though.

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.

If you have this content in user.js then that explains why you get those tabs on the next start.

What other content is in user.js as that might explain what software creates this file ?

This is all the user.js file says:

user_pref("devtools.chrome.enabled", true); user_pref("devtools.debugger.prompt-connection", false); user_pref("devtools.debugger.remote-enabled", true);

That is about enabling the command line in the Browser Console and enabling the Browser Toolbox, so that shouldn't cause this issue. Only a line that sets browser.sessionstore.resume_session_once = true could cause issues with session restore. That leaves options like Firefox not closing properly or a problem with sessionstore.jsonlz4 in the profile folder.

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

You can check for problems with the sessionstore.jsonlz4 file in the Firefox profile folder that stores session data.

• delete sessionstore.jsonlz4 and sessionstore.js

When sessionstore.jsonlz4 is deleted you lose pinned-tabs and open tabs and you will have to recreate them, so if necessary make a note or bookmark them. sessionstore.jsonlz4 is only present in the Firefox profile folder when Firefox is closed.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Neither of these options has worked. I deleted both of these files and used the exit button in the 3-bar menu and it did not work. I have discovered that my computer does this with all web browsers on my computer (Chrome, Firefox, and Edge). Firefox also always pops up with the window that says "Firefox is running but not responding" whenever I try to open a link from another application.

Edit: I also noticed that there is a file called Telemetry.FailedProfileLocks.txt. The number in this file increases each time Firefox closes after I start it up. I tried deleting the parent.lock file but it did nothing.

What is the content of sessionCheckpoints.json in the profile folder ?

This file stores the progress of closing Firefox and all tasks should have finished properly.

The sessionCheckpoints.json file says: {"profile-after-change":true,"final-ui-startup":true,"sessionstore-windows-restored":true}

Edit: I opened and closed firefox again and now it says: {"profile-after-change":true,"final-ui-startup":true,"sessionstore-windows-restored":true,"quit-application-granted":true,"quit-application":true,"sessionstore-final-state-write-complete":true,"profile-change-net-teardown":true,"profile-change-teardown":true,"profile-before-change":true}

I have also noticed that this happens with all browsers accept internet explorer on my computer. This makes me think that it is a problem with windows, not firefox.

I assume you close all tabs before quitting. If so, you may also have to delete "All browsing and download history".