It uses a list of sites, the ones that are in your browser history are red squares. The results may be wrong for you if you cleared your browser history, or if you share your browser with someone else, or if you habitually visit sites you don't like.
Yes. Apparently I don't visit many programming websites, although that's mostly what I do, and I visit more gaming sites than anything. (I only play mario kart on my Wii occasionally.)
