Is your question about restoring data via Sync after you have reinstalled Windows? Note that Sync isn't designed to be used as a backup device, but merely to sync data between multiple devices. It is not guaranteed that you can restore data from the Sync server in case of problems with your OS or because you otherwise lost data. Requesting a new password because you forgot it or changing the password for the Firefox Sync account will wipe all data stored on the Sync server and you won't be able to retrieve data that was stored previously. Best is always to backup your personal data locally to be sure to be able to recover from issues. You can check if you have a "C:\Windows.old" folder with personal data from the previously installed Windows version. * C:\Windows.old\Users\<user name>\AppData\Roaming\Mozilla\Firefox\Profiles "AppData" (XP: Application Data; Mac: ~/Library; Linux: ~/.mozilla) is a hidden folder. *http://kb.mozillazine.org/Show_hidden_files_and_folders *https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile