content: Dude, it says it right on the help section  About this Add-on This extension hides private and important metadata of your browser, usually obtainable using resource:// URIs, against the Web. You should have it installed if you use many extensions, because having many extensions means having many tracking and fingerprinting vectors. Also, Web sites can generally probe Firefox for installed extensions in many cases without this. The extension makes that privacy threat less effective. It may break some extensions which depend on this leak.