You are right! In this case the discussion is really useless.
If your only device to administer the internet access device ( IPFire ) is a dedicated process control display ( with associated IPC ), you cannot really configure the firewall.
In terms of security it isn’t acceptable, that IPFire configurations are done from an normal user device. Those tasks should be done by the administrator only from his own device. Access to this device must be controlled by policies ( not in the electronic system ).
Regards,
Bernhard