Earlier this year, the Windows Live Messenger team released an app for Facebook which officially integrated Live Messenger with Facebook. The Windows Live Messenger Facebook app shows your online presence on your Facebook profile and lets you IM with your friends directly on the Facebook web site itself.
Recently, this app received an update. The new V.2 version of Facebook Messenger now syncs your Live Messenger status with your Facebook status. The team also listened to user feedback and removed the HIP (Human Interface Proof) challenge which was presented before you could start a conversation.
Additionally, the new version will automatically set your display name to whatever your name is in Facebook. Before it used to prompt you to fill this in. With these updates (both the HIP and display name), there are now no more dialog boxes that appear before chatting can begin. You can now just start typing to IM your friends!
You can add Live Messenger to your Facebook by adding the app here: apps.facebook.com/windowslivemessenger.