Have ix-input with type="number".
Open the form in Firefox
Type "asdf"

ER: I am not allowed to type "asdf" or I see a validation error.

AR: I don't see an error and can save the form.

Note: It seems that although Firefox allows user to enter letter, it will only emit proper numeric value in (input) event. Confirm this and figure out a way to clean the input. Ideally ix-input will take care of it and will only return clean value to parent forms.
A potential solution may be to use :invalid css property https://stackoverflow.com/a/18853866