On each and every webpage you visit, it’s more than just that website peering at your activity. Ad networks, social networks, analytic services, cookies, “invisible pixels”—they’re all tracking your moves, to the tune of dozens of watchers per webpage in the worst cases.
Disconnect and Ghostery put a stop to that, identifying exactly who is tracking you and granting granular controls to allow it or nip it in the bud. Disconnect offers some additional bells and whistles such as the ability to speed up browsing times or force secure connections with popular websites, while Ghostery can block scripts and interactive objects from untrusted sources. Both extensions perform the core spy-squashing activity equally well, however. Pick one!