This page provides some tools for testing out your browser and network configuration for WebRTC capability.
STUN-only connection test
This section attempts to initiate a WebRTC session strictly using STUN. Below, you will see a few port numbers listed.
If at least two of the numbers are the same ("cone-ish" NAT), you should be good to go! If all of the numbers are different ("symmetric" NAT), you will likely have trouble with peer-to-peer connectivity.