Hi,
Could you please confirm that oyu are able to submit the form in other browsers? I have never seen this behavior before.
Which version of Kentico
CMS and FireFox do you use?
Do you use Alternative form for the bizform? If so, could you please check on the bizform's Fields tab the fields which are set NOT to allow empty value and are set to be displayed in the editing form - are they present in the custom alternative form (or on the live site)?
Because if you do not use this field - which does not allows emtpy value in your alternative form, you won't be able submit the form because the field cannot be empty.
If not, is it possible to see the form online?
Best regards,
Juraj Ondrus