Content moderation by social media companies is a challenge for regulators around the world. The European Union is trying to tackle this challenge with its Digital Services Act (DSA). Notably, Article 14 DSA aims to impose language requirements based on the principle of legal certainty to social media companies' terms and conditions, of which community standards (CS) are a part. The principle of legal certainty is one of the building blocks of international human rights law, and its inclusion in the DSA illustrates the human rights-based approach anchored in this European regulation. Based on a content analysis of Facebook's CS, this paper shows that their standards do not meet European requirements for legal certainty and argues that important changes in content moderation governance would be needed for proper compliance. Such changes could generate a domino effect beyond the European Union and on Facebook's content moderation governance itself. At the same time, the DSA could also generate a boomerang effect on the legal certainty principle as such. From this perspective, the paper contributes to the literature on regulatory governance studies, and on international human rights law in social media studies from a European Union perspective.