For the bookmarks you can restore a recent backup in the bookmarkbackups folder. *https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them Other data can only be restored if you have a backup. You can look a utility to browse System Restore points. *https://www.shadowexplorer.com/ *https://www.nirsoft.net/utils/shadow_copy_view.html You can check if you have a C:\Windows.old folder with your Firefox profile data. You can check if you have an "Old Firefox Data" folder on the desktop when the Refresh feature in Firefox has been used and a new profile has been created. *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile