Hi Mark, sorry to hear it's not working.
I searched for your IP in the master server logs and found the errors -- it's saying it can't connect to your FSHost at all, as you said. I think the reason why you don't have a problem using IE is because it's making an outward connection, which as you probably know, routers usually don't have as much of a problem with.
It sounds like you've done everything you're supposed to though. Have you verified your external IP address with the one that's being reported in the FSHost error message, just to be sure that the master server is seeing it correctly? You might try
http://www.whatismyip.com.
You also mentioned that you set the router to accept all ports for your machines -- I wonder if it'd be worth a test to also add the IP of the master server, which at the moment is: 217.116.225.78
Are people able to get to your FSHost public web page? I'd guess not, but it's something to check also, in case it's just the master server that can't see it.
Also, are people able to connect to your FSHost with FS?
Russell