Usually Sync still has your data. Did anything come back -- bookmarks, other logins? Did your Windows reset store your old data in a new temporary folder called C:\Windows.old '''Can you find such a folder on your system?''' ''If so:'' Before proceeding, please set Windows to show you hidden files and folders: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files Then check here: C:\Windows.old\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles\ You might just have one profile folder, or you might have more than one. One way to tell whether a profile was one you were using recently is to check the date/time stamp on a file like '''places.sqlite''' or check the dates in the file names in the '''bookmarkbackups''' folder. Anything there that we could work with?