The test page would have worked for anybody not only LimeWire. However that page is no longer active.

Only port test I can find that still seems to give a reliable response is this one: Shareaza Connection Test

How to use? Open FrostWire. Go to your Tools -> Options -> Advanced -> Firewall/Listening Ports & see which port FW is trying to connect through. Copy paste that port into the port test page. Run the test whilst FrostWire is open. If TCP is open then all is good.