Facebook outlined new rules today designed to stop users from illegally selling guns through its social networks. In a blog post, the social network giant said that it will limit posts on Facebook and Instagram discussing the sale of firearms to users over 18, warn people promoting the private sale of weapons to comply with relevant laws, and introduce “in-app education” on Instagram for those who search for gun promotions or sales. The new policies will be implemented and enforced in the next few weeks.