A checkbox is just a little element of a HTML page.
There must be some code in associated .cgi file to realize the function. Maybe someone wants do the coding.
IMO, this functionality isn’t very urgent. Allowing access to the IPFire WUI isn’t really a security problem.
Without credentials ( which are not shared by the admin, hopefully ) one can do nothing.
On the other side, a strict denial closes out the admin too.
EDIT: changed my answer according to TO’s problem. My first answer related to the problem of immediate blocking in firewall. 