Are you talking about the form filler built into Firefox? https://support.mozilla.org/en-US/kb/automatically-fill-address-and-credit-cards https://support.mozilla.org/en-US/kb/control-whether-firefox-automatically-fills-forms

To show the menu bar you need to right-click a tool bar and select "Menu Bar" OR tap the (left) alt key.

Suggestions in a login drop down list that have a key icon in front are login suggestions that you need to remove in the Lockwise 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