If you changed your Firefox Account password after reinstalling Windows and Firefox, but before you were able to recover you data from Sync; I am sorry to inform you that your data is gone. Changing the FxA password wipes your data from the Sync server; for your security and to allow you to get a fresh start if your data corrupted. You should have got a warning about your data being cleared before it happened, along with needing to approve that action or to end that procedure. Now, if you do have another device connected to that same Sync account your Firefox data, let us know and we can help get Sync up and running again to restore you data back into the Sync service. Sync is not intended to be used as a backup media for a single device when the user reinstalls their operating system and all their programs.