Do you mean authenticate the firewall ports before passing any traffic? if that is the case why would you want to do that? the firewalls have their own security features to protect themselves and they are devices that you connect to specific switch ports with no dynamic movement or attributes. Dot1x needs a supplicant to go through the authentication process which doesn't exist on the FTDs. Although in theory you would be able to get away with MAB but again I don't believe that would be recommended nor adding any security to your firewalls.
If the idea behind your question is to restrict the unauthorized accesses to your firewalls then you can set some restrictions on the firewalls management interfaces including the allowed IP addresses as well as the authorized users and if you don't have any management services running on the data interfaces no one could leverage those interfaces for management accesses.
