I think I might have missed an important step. What happened to the contents of your computer between the time that Windows 10 went down and the time you installed Firefox again? If you used one of the options to refresh Windows, hopefully your Firefox data was saved. Here's how I suggest looking for it. First, please turn on viewing of hidden files and folders: http://windows.microsoft.com/en-us/windows/show-hidden-files Then check in these locations: * C:\Users\''your-user-name''\AppData\Roaming\Mozilla\Firefox\Profiles ** How many semi-randomly-named profile folders do you find in this location? If there is only one folder, it's likely your current one that doesn't have your data. * C:\Windows.old\Users\''your-user-name''\AppData\Roaming\Mozilla\Firefox\Profiles ** Can you find any semi-randomly-named profile folders here? If so, one of them most likely has your latest pre-upgrade settings. Based on what you find, we can suggest the shortest set of next steps.