Dispatch event through DOM event interface

The nsIDOMEventTarget and nsIDOMEvent interfaces allow one to dispatch
synthetic event to certain element at target. This is working fine for
triggering event handlers. However, I find these simulated events
don't change focus, selection ect. For example, if I simulate a click
on a text node at certain screen location, the onclick handler will
fire on the parent of this text node, but the caret won't move there.
Similarly, a simulated click on a button won't switch the focus to the
button. Is there a way to achieve those? Thanks.