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

You may be in Private Browsing mode or told Firefox not to remember.

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.

Macs: Make sure you install Firefox properly and that you do not run Firefox from within the DMG (Disk Images) file. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

With no disrespect to FredMcD, these are the same instructions available on many forums and they DO NOT work. Someone needs to look into this problem. For me, I've been through all the troubleshooting, changing of settings, uninstall/reinstall. I've compared all settings between my desktop and laptop and they match. No matter what, Firefox always signs out of sync when Firefox is closed on my desktop, laptop stays signed in.

The credentials to login to the Sync account are stored in the Password Manager (logins.json), so if you have to login again after starting Firefox then it sounds that your Password Manager isn't working or otherwise the logins.json file gets cleared

This chrome://FirefoxAccounts entry is hidden from Lockwise, so you can only see it if you inspect logins.json directly.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data