Port 5060 is for the SIP protocol. It's commonly used in VoIP applications. The problem with SIP is that it doesn't behave nicely with the NAT in almost all home routers, so home router manufacturers commonly implement what's called an ALG (application level gateway.)
The key passage in the wiki entry is "An ALG is very similar to a proxy server, as it sits between the client and real server, facilitating the exchange. There seems to be an industry convention that an ALG does its job without the application being configured to use it, by intercepting the messages. A proxy, on the other hand, usually needs to be configured in the client application. The client is then explicitly aware of the proxy and connects to it, rather than the real server."
What that means is that port 5060 on the router is expecting just SIP traffic, so in many cases if it sees non SIP formatted traffic, it doesn't know how to pass it through. Think of it this way... A fully open port with no firewall blocking is like an open door for all traffic and a blocked port is like a locked door for all traffic. But a port configured with an ALG is like a closed door that automatically opens for SIP traffic but stays closed for all other traffic.
So there are two key questions:
 Is there any config setting in the router to disable or get past this ALG
 If 5060 is blocked does that truly have any impact on LOL?
I don't know the answer to #2, that would be something for the LOL techs. But for #1 you might want to hunt around in your router config to see if there are any sort of SIP related config options.
If you find a config setting to change, then re-run the firebind test to see if that got you past it.