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.

Is the Firefox Password Manager working properly?

Firefox uses the Password Manager to store the credentials of the Firefox Sync account (chrome://FirefoxAccounts). If you are asked to login again to Sync or another service then this means that this data isn't stored in the Password Manager.

You can try to disconnect and reconnect Sync.