Changing the port that Shoutcast uses should solve the problem.... I haven't tried to shoutcast and run FF at the same time before. But that seems to be the most logical solution... it sounds like FF is using ports 8000 and 8001 they go in pairs like that so if you change your port in shoutcast to something other than 8000 say you use 8002 for example as long as that doesn't conflict with something you should be good to go.
But, you do have to modify the Configuration file for the Server program to reflect the change made in the Shoutcast Source.