Both Mozilla and Google consider their browsers to be shims for the underlying OS. Firefox OS and Chrome OS betray that assessment. Accordingly, IE has been

Both Mozilla and Google consider their browsers to be shims for the underlying OS. Firefox OS and Chrome OS betray that assessment. Accordingly, IE has been historically crippled by Microsoft because they realize that browsers obsolete operating systems in many important ways for end-users. Consider that operating systems are tremendously sophisticated user-facing applications in their own right, and that dwarf the high level "web browsers" they support in complexity. ;)