Are you referring to a name and password that is saved in the password manager? *Tools > Options > Security: Passwords: "Saved Passwords" > "Show Passwords" In that case you need to remove the old name and save the new name when Firefox asks you to remember a new name and password. *https://support.mozilla.org/kb/make-firefox-remember-usernames-and-passwords ---- If you want to remove saved form data from a drop down list then use these steps: #Click the (empty) input field on the web page to open the drop down list #Highlight an entry in the drop down list #Press the Delete key (on Mac: Shift+Delete) to remove it. *http://kb.mozillazine.org/Deleting_autocomplete_entries