Go into your Browser, clear your history and yoru cache. You have to remember EVERY site on the internet is linked to Facebook. You click an article, it is linked to Facebook. You click on another article there is a like button or a like us on facebook button.
It isnt a setting, it isnt part of the host files. It has nothing at all to do with your setup. You forget that the world is plugged into Facebook. Just cause you dont dare go there on a work PC doesnt mean that the rest of the world will cater to you.
Strange this is the same suggestion that was the very first response. The whole clean out your cookies/cache/history. Did you bother to do it way back then?
This is not anything associated with IE9 at all. Cause if it was, then more people would have experienced this. Since that has been the only browser i have used since it was released, and i dont have those listed in my back button, it is not related to the browser or any of its settings. It is something specific to your machine and your setup.