FC3: firestarter + dynamic DNS hostname = trouble

I'm using firestarter in FC3 to config the firewall and it seems great.
Only problem I've ran into is that I'm wanting to create a rule based on
a dynamic DNS hostname (using the dyndns.org service).
So I make a rule allowing the host somehostname.dyndns.org access
(having set up this address with dyndns.org previously), but it wasn't
working. I did iptables -L to see what was going on and I could see that
firestarter has done an IP lookup on my hostname, and then done reverse
DNS lookup on that, and got a different hostname which is IP-specific of
the form:

hostXX-XXX-XXX-XX.rangeXX-XX.btcentralplus.com

^^^ contains the actual current dynamic IP address!

Is there a way to tell firestart not to mess around with the hostname I
give and just accept it verbatim?
Should I think about editing the iptables directly?

ta
alex