Do you have a backup of the new Sync key or the Sync key that was last used with that Sync account?

Note that when you reset or regenerate the Sync key that you lose all data stored on the Sync server.

• https://support.mozilla.org/kb/how-do-i-manage-my-firefox-sync-account
• https://support.mozilla.org/kb/ive-lost-my-firefox-sync-account-information

Hi, thanks for replying I have my Firefox Sync Key what to do??

Please i need help

You need to access your old Sync account.

Enter all details like the account name (email address) and password and the 26-character Sync key manually to connect to an existing sync account.

1. open "Firefox > Set Up Sync..." or "Tools > Options > Sync > Set Up Firefox Sync"
2. click "I Have an Account"

That brings you to the "Pair a Device" window.

• click "I don't have the device with me" at the bottom to enter the account settings (email, password, sync key) manually.

thanks again for your answer but now i am using Firefox nightly and now it is just supporting the new sync not the old so i cannot reach the old sync

Thank you problem solved by installing the main release of firefox and run syncing then re login

thanks