WebRTC IP Leak Test

Web RTC:

If you are connected to a VPN and in the Web RTC: section you see your ISP IP, then your system is leaking WebRTC requests
If any IPs match with one of your LAN Private IPs you will have a partial Leak

WebRTC Browsers have implemented WebRTC that allow requests to STUN servers be made that will return the local and public IP addresses for the user. These request results are available to javascript, so you can now obtain a users local and public IP addresses in javascript. This demo: https://ba.net/adblockvpn/webrtc-leak/ is an example implementation of that.

Additionally, these STUN requests are made outside of the normal XMLHttpRequest procedure, so they are not visible in the developer console and cannot be blocked by plugins such as AdBlockPlus or Ghostery. This makes these types of requests available for online tracking, de-anonymize and trace users behind common privacy protection services such as: VPN, SOCKS Proxy, HTTP Proxy and (in the past) TOR users.

How to disable WebRTC in Firefox?
In short: Set "media.peerconnection.enabled" to "false" in "about:config".

Explained:

Enter "about:config" in the firefox address bar and press enter.
Press the button "I'll be careful, I promise!"
Search for "media.peerconnection.enabled"
Double click the entry, the column "Value" should now be "false"
Done. Do the WebRTC leak test again.
If you want to make sure every single WebRTC related setting is really disabled change these settings:

media.peerconnection.turn.disable = true
media.peerconnection.use_document_iceservers = false
media.peerconnection.video.enabled = false
media.peerconnection.identity.timeout = 1
Now you can be 100% sure WebRTC is disabled.