It's been a hot year for Facebook — the company bought the virtual reality company Oculus and the messaging app WhatsApp for a combined $24 billion, and Instagram, which it bought for $1 billion in 2012, is now valued at $35 billion. But Facebook has also matured as a platform for brands to promote and sell their content: Retailers, in particular, have enjoyed Facebook's referral system, especially leading up to the all-important holiday season.