When you have an "Old Firefox Data" folder on the desktop then the Refresh feature in Firefox has been used and a new profile has been created. *https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems In your case it looks that something went wrong and that Firefox failed to create a new profile or failed to update the profiles.ini file. You can use the Profile Manager to create a new profile. See "Creating a profile": *https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems. *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox ---- You can copy some files with Firefox closed from the "Old Firefox Data" folder on the desktop to the current profile folder to recover specific data. *bookmarks and history: places.sqlite *bookmark backups: compressed .jsonlz4 backups in the bookmarkbackups folder *cookies.sqlite for the cookies *formhistory.sqlite for saved form data *logins.json and key3.db (decryption key) for Passwords saved in the Password Manager *cert8.db and possibly cert_override.txt for (intermediate) certificates stored in the Certificate Manager *persdict.dat for words you added to the spelling checker dictionary *permissions.sqlite for Permissions and possibly content-prefs.sqlite for other Site Preferences *sessionstore.js for open tabs and pinned tabs You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page. *Help -> Troubleshooting Information -> Profile Directory:<br>Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder *http://kb.mozillazine.org/Profile_folder_-_Firefox