That doesn't sound good. Can you provide more details? Was it a windows reinstall? Is there a 'windows.old' folder on the drive?

the is a windows.old but it is empty, my disk C is 49 Gb but still I don't where else it stored my files. I reinstalled firefox hoping that my bookmarks, and logins will be kept in the account but nothing happen when I log in the browser. Is there any step I dhould have take?

Note that sync isn't designed to be used as a backup and you can always be unlucky if you rely on restoring data via Sync. Best is always to backup your personal data locally.

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Also if you did have the reset the password of the Sync account, you also lose your personal data.