[djeric3]

Facebook.com today loads functionality dynamically. Open the Network panel, interact with a secondary feature, and you will see it load code on-demand.

With respect to your example of unnecessary modules, sometimes the dependency trees between modules are non-obvious. But more to the point, the code served to a user is NOT personalized for each individual user and to their specific newsfeed and UI contents. This is actually a performance optimization. Facebook looks at which modules are most commonly required across most users based on their recent activity, and then bundles those common modules into large packages and pushes them aggressively to the browser. This actually results in a very large loading-time win, but ends up overserving some % of extra modules that are not needed by a specific user.