So the beacon tracks a user by their IP address and browser client information. Advertisers/marketers have you put a 1px x 1px transparent GIF or PNG image on your pages or in an email blast. The image is hosted on their remote server. Then the remote server put your information into a database. By cross-referencing your IP browser agent information they can track you by without creating a cookie, local storage, or indexed database anymore.
At least the Mozilla foundation is trying to to create an Opt-Out standard. But who says any of them will adopt this standard.