[seanp2k2]

You can see EFF PrivacyBadger code getting injected in the source tab in dev tools, not positive about network requests. It wouldn't be hard to test though, just make a simple extension that does XHR to example.com and load it up locally. Chrome extensions are surprisingly easy to write, and there are some simple tutorials if you google around a bit :)

EDIT: here's how to inspect extensions you're curious about: https://developer.chrome.com/extensions/tut_debugging