From MozillaZine Knowledge Base
Ports are used when any program accesses the Internet so that the system can keep separate applications' data separate. Some port numbers are reserved for functions such as e-mail or FTP. To prevent potential security risks if a protocol was allowed access a port reserved for a seperate protocol, Gecko applications contain a list of banned ports. This preference allows you to unban a port banned by default and therefore prevent the "Access to the port number given has been disabled for security reasons." or "This address uses a network port which is normally used for purposes other than Web browsing. Firefox has canceled the request for your protection." messages.
Possible values and their effects
A comma delimited list of port numbers to allow.
First checked in
Has an effect in