I am thinking two possibilities.

1) 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.

2) Your ‘logged-in’ status is stored in special cookies. If the cookie is removed, you are logged out.

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

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.

I tried number 1 and that did not seem to work, I do not have any protection software. and number 2 I have that exact setting chosen. When I had Google Chrome before I did not have this issue

Is this about connecting to Sync ?

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 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 have security software that might be deleting the passwords? Are only the passwords lost or is there more personal data affected?

Location used for the main profile that keeps your personal data (Root Directory on about:profiles).

• ~/Library/Application Support/Firefox/Profiles/<profile>/

I have the same issue. No security software. I use Firefox Developers Edition and everytime I shut down the computer and start again then firefox wants me to log in my sync with email confirmation...

a-dante Have you tried the above?