Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
The :-moz-submit-invalid CSS pseudo-class is a Mozilla extension that represents any submit <button> on forms whose contents aren't valid based on their validation constraints.
By default, no style is applied. You can use this pseudo-class to customize the appearance of the submit button when there are invalid form fields.