If it wasn't bad enough that Facebook bought FriendFeed on Monday and turned on real-time search to better compete against Twitter in the Stream Wars, and is playing around with a lite version that resembles Twitter even more, now Twitter really has something to worry about. Facebook is growing faster than Twitter in the U.S., even though it is more than four times larger. In the month of July, according to the latest estimates from comScore, Facebook attracted 87.7 million unique visitors in the U.S., which was 14 percent higher than in June, 2009.