Did you try to connect your new installation of Firefox to your old Firefox Account? That's covered by the second section of this article: [[How do I set up Sync on my computer?]] If that did not work... What kind of reinstall did you do? Sometimes Windows will create this folder: C:\Windows.old That is a temporary folder (removed after 28 days) with a copy of a lot of your old data in it. Let us know if you find that. To explore its contents fully, you'll need to set Windows to show hidden files and folders: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files