The Firefox Sync service really isn't intended as a "backup service" to be used when formatting your hard drive. You need three things to connect a "new" device (which is basically what you have after a format). <br /> # your Sync username # your Sync password # your '''Sync Key''' - which is used for encryption and decryption If you are missing any one of those things, you won't be able to recover your data from the Sync server. Do you have any other devices setup on that same Sync account? <br /> If so, you can get those three things from the Password Manager window in that other device (at least non-"mobile" devices).