Microsoft has been steadily incrementing features and versioning for their internally developed Facebook app for Windows Phone 8 for a long while. For Windows Phone, Microsoft's Facebook app is the best available, and I'd argue that it's probably a better app than on any other platform. I've worked with iOS and Android, so I believe I know first-hand.
Today, Microsoft finally considers the app is ready and has removed the Beta tag from the app's title.
To get it, you can do a search for Facebook in your Windows Phone store app, or drop out to the web version of the Windows Phone store and choose to install it to your Windows Phone device from there: