Comment 3 for bug 1778063

Those are intentional because browsers usually decide that they know best when it comes to usernames and passwords and will ignore the usual autocomplete="off" attribute. When presented with an autocomplete type that they don't know about though, they stop trying to second guess us and leave the fields alone.

Though looking at https://developer.mozilla.org/en-US/docs/Web/Security/Securing_your_site/Turning_off_form_autocompletion it seems that Firefox specifically thwarts this method by returning to the default handling for those fields. :( I was trying to be sure that the browser never tries to suggests a saved set of staff credentials for a new user (or asks to replace staff credentials with a newly created one!) Looks like that may only be true for Chrome and Safari. (For now?)