You can check if you have the <b>C:\Windows.old</b> folder with your Firefox profile data. *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile If you reset the password for the Mozilla account because you do not remember this password, then that will remove all data stored on the Sync server because this password is used to encrypt your data locally before it is uploaded to the Sync server and only this password or a possible recovery key you created earlier can decrypt this data.