Sounds like a Facebook problem more than your MBP. You'll get the beachball anytime OSX is waiting for something to finish, in this case for Facebook to respond. If that's the only place it spins, it sounds like something at your Facebook page is not working. But tell us more about your machine: OSX version, what browser, how are you connected to the Internet, memory installed, etc, etc., and perhaps someone can help you more.