1. Sync isn't intended to be used to backup Firefox data when doing an OS re-installation. It's meant for synchronizing Firefox data across multiple devices. ''The key difference is that your data would be still on another device should you have a problem when re-connecting the newly installed operating system.'' 2. When setting up a Firefox Account for Sync, you are sent an email that requires confirmation to finalize the new account setup procedure. There is no confirmation on the setup page. 3. Whatever you do, don't reset the Firefox Account password. The password is the "key" to your data; reset the password and your data is rendered useless. The password is used to encrypt your data, a different password wouldn't decrypt your data; and the reset clears your data from the Sync server, being that the data is useless and can't be decrypted..