The servers that store the old Sync data have been taken down and can no longer be accessed, so all data stored there is lost. *https://blog.mozilla.org/services/2015/07/31/shutting-down-the-legacy-sync-service/ When you refresh/reset Firefox then a new profile is created and some personal data (bookmarks, history, cookies, passwords, form data) is automatically imported. The current profile folder will be moved to an "Old Firefox Data" folder on the desktop. Installed extensions and other customizations (toolbars, prefs) that you have made are lost and need to be redone. It is possible to recover data from the "Old Firefox Data" folder on the desktop, but be cautious not to copy corrupted files to avoid carrying over problems. The old profile is in this hidden location: *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\ *http://kb.mozillazine.org/Profile_folder_-_Firefox *https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile ---- You can transfer files like these from the profile backup. * bookmarks/history: backups in the bookmarkbackups folder and possibly places.sqlite if you really need the history * other SQLite files like cookies.sqlite (cookies) and formhistory.sqlite (saved form data) * logins.json and key3.db for the passwords in the password manager * permissions.sqlite and possibly content-prefs.sqlite for the Permissions and Site Preferences * cert8.db for stored intermediate certificates * sessionstore.js for open tabs and pinned tabs and tab groups You can restore a JSON backup in the Bookmarks Manager (Library). *Bookmarks > Show All Bookmarks > Import & Backup *https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them *http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox