Do you possibly have a logins-backup.json on any of the connected devices that still have logins ?

Firefox 80+ has a logins-backup.json file in the profile folder that can be used in case of issues with logins.json or to undo an accidental delete/update of a password. You can check if you can find this logins-backup.json file in the profile folder or in a backup.

Make sure to keep a backup of the current logins.json and logins-backup.json before replacing logins.json with logins-backup.json with Firefox closed.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

You can look for older copies of logins.json and key4.db (encryption key).

You can check if you have an "Old Firefox Data" folder on the desktop in case the Refresh feature in Firefox has been used and a new profile has been created.

• https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems

You can look a utility to browse System Restore points.

• https://www.shadowexplorer.com/
• https://www.nirsoft.net/utils/shadow_copy_view.html

Note that you should be cautious with wiping data like logins from the original device as Firefox remembers where they came from and thus propagates this to other devices. Always keep a backup for cases like that.

many thanks on the replies!

I checked on one of the two computers and did not found it even with shadow explorer as the snaps may have been rolled off. one more computer to check but that will take some time to reach. I'll reply once I check it :)

many thanks again! C.

You can change the password of the Firefox Sync account to prevent data from passing to other devices that haven't been started yet.