That could be caused by several different things.

1) 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

2) Type about:preferences#privacy<enter> in the address bar. The button next to History, select Use Custom Settings.

Turn off Always Use Private Browsing Mode Turn on Remember My Browsing And Download History At the bottom of the page, turn on Clear History When Firefox Closes. At the far right, press the Settings button. Turn on ONLY Cache and Form And Search History leaving the others off.

3) https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Firefox uses the Password Manager to store the credentials of the Firefox Sync account (chrome://FirefoxAccounts) to make it possible to connect to Sync each time you start Firefox without the need to enter email and password. If you use the master password then you need to enter the MP every time you start Firefox. If you are asked to login again to Sync then this means that the Sync credential data isn't stored properly in the Password Manager.

Do you see any entries in the Firefox Password Manager ?

• Options/Preferences -> Privacy & Security: Logins and Passwords: "Saved Logins" -> "Show Passwords"

You can check if you have a logins.json.corrupt file in the profile folder.

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 Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/Profiles

Attempted each of the remedies above, and Firefox still will not stay signed in. Even if I just close the window, opening it up will demand another sign in, suggesting I sync and install firefox on my phone, though I have done all of these moments ago. What is wrong with Firefox?