WebRTC creates a security hole in both Chrome and Firefox. Without an addon there is no good way to disable this security hole in Chrome but you can disable WebRTC in Firefox.

First check to see if you have a problem, if this website shows any IP Addresses then there is a webRTC security hole in your browser: https://diafygi.github.io/webrtc-ips/

Disable WebRTC directly by opening a tab and going to “about:config” in the address bar. Find and set the “media.peerconnection.enabled” setting to false.

https://diafygi.github.io/webrtc-ips/ should no longer show any IP Addresses.