ShareMeNot is a Firefox add-on designed to prevent third-party buttons (such as the Facebook “Like” button or the Twitter “tweet” button) embedded by sites across the Internet from tracking you until you actually click on them. ShareMeNot does this without completely removing the buttons from the web experience.
Did you know that buttons like these allow Facebook, Google, LinkedIn, and others to track your online browsing activities on every site that includes one of these buttons, even if you never click the buttons and even if you have third-party cookies disabled?
The FAQ explains why this is somewhat more complicated to accomplish than what ad-blockers generally do.
I wish there was a Safari version.