There are several websites world over that track users. Originally, tracking mechanisms included Cookies, Flash Cookies. Historically too, I have written about Firefox add-ons in the articles below:
Firefox add-ons you should never surf without
Watching you silently – Flash Cookies / LSOs
As mitigation measures were developed to counter cookies and flash cookies, old user tracking mechanisms were no more adequate. The latest method is invisible tracking with the use of Canvas FingerPrinting.
Articles below on the internet indicate that this kind of tracking is almost unstoppable. They also provide the safeguard to stop such tracking.
First attempt with Ghostery. Will post any issues if encountered.