Why use window here and not var builtInRingtones? I don't feel strongly either way and am just trying to understand the stylistic choice here.  Note that a property created with var is not deletable, but one created this way is, if that matters to you.

A stylistic issue that does matter to me is that self-invoking functions like this one should have an open paren before the function keyword.  Since it is 100+ lines before we get to the "();" that invoke this function, the reader can't easily tell whether it is the function or its return value that is being assigned.  Putting an open paren here is a useful convention that it is the return value.