Hey Birdy

You're still right that one cannot direct connect to firewalled hosts.

The firewall icon (brickwall) is what is messed in the 4.15.1 beta. It will show as bricked even when no firewall is active.

In the older versions, the bricks are 'on' until connected to stable ultrapeers, but go away (if appropriate) once connections are stable.

cheers.

stief rocks!
 

I was able to get this working thanks to stief...

The two main problems were:

1. The port forwarding was broken. My computer was using DHCP and had an internal address that was different from all the port forwards set up on the AirPort. (Yes, a stupid oversight on my part.) I had to set my computer to use a static IP address, configuring it manually to use one number higher than the DHCP assignment range. As it was, this was the address all the entries in the port forward list were pointing to originally.
2. Certain port numbers in LimeWire might not work. The original number I was using for the ports (6346) in LimeWire didn't work. Changing it to a higher number (16858) fixed it.

My thanks to stief for his assistance, and to birdy for pointing me in the right direction.