How did you do the upgrade? Did Windows ask whether you wanted to keep your data? Let's check. Windows often creates a temporary folder (retained for 30 days) called C:\Windows.old If you have that folder, your old Firefox data should be inside. To explore that copy of the old user folder, you need to turn on viewing of hidden files and folders: http://windows.microsoft.com/en-us/windows/show-hidden-files Then look for C:\Windows.old\Users\''your-user-name''\AppData\Roaming\Mozilla\Firefox\Profiles Assuming you find one or more folders there, one of them most likely will have the earlier Firefox data. If you check the last modified date/time, does it look promising? If so, we can suggest next steps.