This subdomain denotes Facebook’s mobile-optimized website. Unlike www.facebook.com , which serves a heavier, JavaScript-intensive React-based interface, the m. subdomain is designed for legacy or lightweight mobile browsers. It sends significantly less initial HTML and relies on progressive enhancement.
YOU ARE LOOKING AT THE BLUEPRINT, ELIAS. DO YOU WANT TO SEE THE ARCHITECT?
For developers, viewing Facebook’s source code is an educational tool to understand how high-traffic platforms implement complex features. However, Facebook's code is often "minified" or obfuscated—essentially scrambled—to save bandwidth and make it harder for unauthorized parties to copy or reverse-engineer. HTML Source Viewer (view-source: on Mobile) - Trevor Fox
