manual focus management woes

Context: http://stackoverflow.com/questions/702585/simulating-a-tab-keypress-using-javascript

Gosh, what year is this? I have to do manual focus management for
anything remotely outside the box?

Even if I do, then I have to keep track of everything OUTSIDE my form,
because that's what Tab and Shift+Tab would normally focus on after the
edge elements. Worse yet, I can't even completely emulate the natural
behaviour, because the tab-stops normally include browser UI elements
as well.

Is there seriously no way of having the browser think the user pressed
Tab?

(It's situations like this that I find extremely frustrating when it
comes to web development. I'm trying to make a UI that's as smooth as
possible, nicer to use than the average UI, and I end up re-
implementing everything, or not even being able to if I wanted. All
for something relatively subtle...)