How to undo "Enable autofill for [website]" in Firefox?
External autofill apps change a certain boolean in the Firefox for Android configuration variables, this "setting" can nly set back to the old setting by completely uninstalling and reinstalling Firefox or better by changing it in: about:config


goto about:config
search for: dom.forms.autocomplete.formautofill
set it back to true
refresh your login window and... fixed!