http://payit2cen3j7qjcyfwlgawk5nfeclttnv34sf6swp65irsadxjqgejqd.onion/tracking.html
While software like NoScript prevents this, it's probably a good idea to block this protocol directly as well, just to be safe.
Here’s how to check if your IP Address is leaking: Run this ipleak.net Under heading Your IP address - WebRTC detection does it say "No Leak"?