Any chance that you reset your Sync Password?

yes i reset my sync password

yes i reset my sync password

Your data was wiped from the Sync server when doing that reset. I guess you missed the warning message about that - see the screenshot.

you are right, i missed this message. there is no way to get my data back , right ?!!?? i need this sync, it is very important to me, help me to recover it

Sorry, your data was wiped from the Sync server when doing that Password reset, and unless you have a backup saved elsewhere, I am afraid you're SOL.

The thing is, the Password is used inside Firefox to encrypt your data as it leaves your PC for the Sync server, where it remains encrypted; no one else has access to the "encryption keys" (there are two kA & kB) for that data or can access your data without those two keys. Change the Password and those "encryption keys" becomes invalid; your data can't be decrypted when it arrives back at one of your devices. No point in not deleting that data from the server, it's useless. Plus that action allows the user to keep using their Sync account / Firefox Account without needing to create a new account (using a different email address) to fix an issue with data corruption or if the user needs to delete their data in the case of a lost device - it stops the "thief" by blocking access the users Sync account once the Password is changed.

Overall, Sync is intended to synchronize data between multiple Firefox installations / devices; not intended as a backup media for the purpose of re-formatting as hard drive or re-installing the operating system.

IMO, this "encryption" setup is far more security that the average user needs for any data saved in Firefox other than Password / Login data. I would have liked Sync better if the "other data" was handled differently than the Password / Login data; "double-encrypt" the Password / Login data and allow only the encryption via HTTPS serve to protect the "other data" for the trip to (and from) the Sync server, and don't encrypt that "other data" for storage on the Sync server.

Doing it in that manner would allow the user to recover their data - minus their Login /Password data - if they Reset the Firefox Account Password inadvertently and didn't read that warning message. Face it, IMO people don't read those messages or don't comprehend the meaning of a message like that, all too often - "click it" to make it go away and "move on". And this is continuation of a similar issue that users didn't "get" with the older version of Sync; they neglected to save the Sync Key / Recovery Key and lost their Sync data in another manner; requesting a new Sync Key. The change from 3-factor authentication credentials to a "normal" 2-factor setup eliminated one "problem", but created a new "problem", IMO.