hello, when you reset the password for async account you bascially throwing away the only key to decrypt your exisitng data on the server - the account is reset by that and all data on the server is wiped, so there is no way going back...

Why? Why would anyone think that is smart? And there was no warning that this would happen. This is really dumb.

the purpose of sync is not that of a backup service but to keep multiple devices on the same level.

your sync data is encrypted by a key derived from your account password locally on your device, before it is sent-to and stored on mozilla's sync servers. because the firefox sync architecture is designed with your security and privacy in mind (as it can store very sensitive data like passwords and history), your password will be the ONLY way to decrypt sync data. without your passwords there is no way to access that encrypted data for mozilla either... so a change password will mean a loss of data stored in the sync account - there is a warning about that before the reset procedure!