Facebook has been testing small stickers in comments among a select group of users. Given the popularity of emoji icons and memes and gifs in communicating ideas worldwide, this could be something that adds an additional fun element to their website that people are already familiar with and actually want to use. The more time people spend on Facebook making and reading comments, the more valuable Facebook becomes to its users and the better that Facebook will perform for advertisers.
Facebook has been adding some relatively minor new features to its website lately such as a Save For Later Button. None of these new features are groundbreaking game-changers, but every little minor enhancement adds up to an even better user experience and the possibility that they'll stumble upon something that their users love.