WebRTC Externals is a WebExtension that aims to allow much of the same workflow that developers are using on Chrome's webrtc-internals internal page. However, it is implemented as an extension and therefore does not rely on any internal infrastructure. As a result, it can be run in other browsers like Firefox or Microsoft Edge.
To debug a WebRTC call, make sure that the background page is open by clicking the WebRTC icon labelled "Debug WebRTC" in your browser. Then make a call on a page like one of the WebRTC samples. You should see a an API trace like shown in the WebRTCHacks blog post as a result.
The content script only overrides RTCPeerConnection and not the Chrome legacy RTCPeerConnection. If the site you are testing is still using the old variant you might suggest they upgrade.
MIT
This project reuses large parts of rtcstats.js which is licensed under the MIT license. The files webrtc-internals.js, utils.js and background.html are taken from Chrome's webrtc-internals page and licensed under the BSD license. See NOTICE.md for details. The WebRTC logo was taken from the WebRTC Google Plus page