You are about to follow a link, put the mouse over it, and a f*ing pop-up appears next to the pointer, showing you a preview of the page that link leads to. Something like this

Most of these pop-ups (actually, all I've seen) are created through Javascript; such functionality is provided by a site called Snap. A tip for getting rid of them suggest blocking the .js responsible for the popups, using the browser's utility to block ads; unfortunately, the URL of the offending JS code used nowadays is different, so I had to use a more general pattern.

http://*.snap.com/*.js*

Obviously, your browser might have a difficult time when you visit snap.com. But who cares?

Just for the record: they (Snap) offer a way to disable the snapshot "functionality", using a cookie from their site. I tested it in Opera, and it didn't work, despite of reloading the page and clearing the browsing cache.