Facebook A/B Testing

«Facebook is either A/B testing the hell out of their mobile app navigation or using an algorithm (based on people’s behaviors, regions, strategic/promotional considerations, machine learning models?) to create personalized navigation menus for its two billion users. To learn more, please share your Facebook mobile navigation here and any useful notes (device, operating system, country/region what features you use, etc.)».

Source : Facebook Mobile Navigation – Google Docs