Block the Web spies
More and more websites are filled with small pieces of code existing on different sites and following you around, usually with the aim to make statistics or advertising.
The Ghostery extension will block all trackers, sharing tools and social networks votes, and even some advertising (which can also follow you from one site to another if they use the same ad network).
The resemblance is obvious with AdBlock. Ghostery is less customizable than its predecessor AdBlock, but it's easier to configure and a tooltip will tell you what is blocked. You will be amazed at the number of trackers that follow you everywhere!
But blocking a particular element is impossible if it's not in the predefined list. Unfortunately it is impossible to add filters as we can with AdBlock, so use both extensions if you want to be 100% effective (what I do).