The important thing is, you have to remove all of your devices in Connected Services, including the one with the synced passwords (passwords won't disappear). And them sign in again, starting with the one with passwords.
I found a solution here: https://support.mozilla.org/bm/questions/1268839Copying below in case it disappears."I resolved this issue with the following steps:Browsing to: https://accounts.firefox.com/settingsClicking on 'Show' for 'Devices and apps'Cl...
