Do not confuse the Primary Password that is used to encrypt logins stored in logins.json in the Firefox profile folder and the password for the Mozilla Account used for Sync. *https://support.mozilla.org/en-US/kb/reset-your-primary-password-if-youve-forgotten-it The Primary Password is used only to unlock the logins stored in the Password Manager and is used locally (not part of Sync) and is profile specific. *https://support.mozilla.org/en-US/kb/using-primary-password-sync If you cancel the PP prompt, Firefox won't be able to connect to the Sync account, but otherwise Firefox will work normally.