(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.
(2) In the search box above the list, type or paste insec and pause while the list is filtered
(3) Double-click the security.insecure_field_warning.contextual.enabled preference to switch the value from true to false
(4) Double-click the security.insecure_password.ui.enabled preference to switch the value from true to false
DONE
Basics 