It's because these social media sharing buttons can be used to track you even if you do not click on them.
> For example, when you are logged into your Google or Facebook account and visit a movie review page on rottentomatoes.com, your browser automatically pulls in the "+1" button from Google's servers and the "Like" button from Facebook. These downloads include the session cookies your browser uses to inform Google and Facebook that you have previously logged in, and so Google and Facebook automatically learn about your personal interest in the movie page you're looking at, even if you never actually click on either of their buttons.
There are Firefox plugins like ShareMeNot and Priv3 that block these tracking cookies.
Also, Ghostery belongs to "Evidon", previously named "The Better Advertising Project", and they collect your data and provide it to advertisers...
Slap some priv3 in there too while you are at it.
I would also like to let you guys know about a pretty new tool developed at Berkeley called Priv3 - it allows you to stay logged in to social networking sites but prevents them from tracking your browsing history through those (incredibly annoying) widgets that are EVERYWHERE ("Like", "Follow"", etc.)
Every site that has the Like button allows Facebook to track you, whether you click it or not. This addon blocks the tracking unless you click the Like button. Works for Google+ +1 button too.
Try Priv3
It autoblocks all those "like" and google-thingys from getting your info, but you are still able to if you click manualy that button.
keep all features, don't give them your info
If you visit any site that has a "like" button you will get tracked.
and
Should help with it. Also remember to check if you are not leaking your IP through webrtc