It would be helpful if you show us what you are talking about. Make sure to block any personal info from showing. Is it the saved login prompt from Firefox or the Google prompt? If it's the saved login information from Mozilla, just go to the about:logins page, find the login you want to delete, and delete it.

Password Manager - Remember, delete and edit logins and passwords in Firefox

Suggestions in a login drop-down list that have a key icon in front are login suggestions that you need to remove in the Password Manager.

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins

Suggestions in a drop-down list without a key symbol are autocomplete saved form data. Suggestions without a key icon are part of autocomplete saved form data that you should be able to remove by selecting this item with the cursor Down key and pressing Delete (Mac: Shift+Delete).

• https://support.mozilla.org/en-US/kb/control-whether-firefox-automatically-fills-forms