It also will leak your true IP even if you are using VPN
This demo secretly makes requests to STUN servers that can log your request. These requests do not show up in developer consoles and cannot be blocked by browser plugins like AdBlock, Ghostery, etc.
And that will kind of make all the money you use on VPN.. wasted.
There is a plugin in Firefox that will turn off Webrtc for you it is called WebRTC search for it and install it you can then turn on or off Webrtc as you like.
Tho check if you are "leaking" go here:
With the extension active you will see no IP and when you turn it off - your IP's will be there.
I tested my Betternet VPN plugin and found out that it was not working at all! - It indicated that it was active but it was not so those VPN Browser-plugins are not very reliable.
With my real VPN configured with OpenVpn and NM - and service provided by cryptstorm -WebRTC would not leak my real IP - only the one provided by the VPN service so I did not need the Webrtc plugin for that.
But my internal IP's were leaked (10.0.0.10 and 192.128. etc) - these were hidden with the Webrtc extension activated.
So with Cryptstorm VPN and Dnscrypt; Webrtc will not leak your IP only your internal IP's. With WebRTC addon it will leak nothing.
If you use the WebRTC Network limiter plugin in Chromium and set it to "Best Network experience" then it will leak everything even if Betternet is activated.
Use the "proxy if present" option and Nothing will leak.