If you didn't format the hard drive or otherwise reinitialized the file system then Firefox should have found the Firefox profile folder automatically, so it sounds that you lost your personal data Do you have a backup of the location where Firefox stored your personal data? * C:\Users\&lt;user&gt;\AppData\Roaming\Mozilla\Firefox\Profiles\&lt;profile&gt;\ Note that the "AppData" folder in Windows Vista and later Window 7+ versions and the "Application Data" folder in XP/Win2K are hidden folders. *http://kb.mozillazine.org/Show_hidden_files_and_folders If you do not have the files in the profile folder of your previous setup then your data is lost. ---- If you still have access to the files in your previous profile folder then you copy some files to the current profile folder.<br /> That would be places.sqlite for the bookmarks and history and the two files signons.sqlite and key3.db for the passwords (key3.db stores the encryption key and need to match signons.sqlite). *http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox *http://kb.mozillazine.org/Password_Manager *https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Thanks a lot for your answer - excellent tip, everything is fine !