I have tried BNn, Fczbkk's suggestions and neither solved the problem. Gelatin's mentioned script seems to work but impacts the main window too-you can't see the list of people who clicked on "like" on a post. I have also tried [Yahoo Answers](http://answers.yahoo.com/question/index?qid=20080621140431AAxcbXv) idea to repeatedly click on x's. They disappear momentarily but then again appear next day.

What it works is to install the Firefox add on [FB Purity](https://addons.mozilla.org/en-US/firefox/addon/fb-purity-cleans-up-facebook).
It cleans up the sponsored page, the People you may know and has settings on what you want to appear on Facebook page. I will update my answer if it stops working.