Rated 2 out of 5 stars

It's an extension, meaning that you can find the source code in your ~/.mozilla/firefox/ profile.

Two concerns: The author indeed omitted to add references to the GPL or other open-source licenses. Thus, currently you cannot touch the code.

One of the javascript files is obfuscated, specifically the firefox@ghostery.com/chrome/content/ghostery-bugs.js file.
My concern would be why this file is obfuscated.

This review is for a previous version of the add-on (2.0.2).