I just had one of those times when I thought I totally lost the ability to do simple logic. Take a look at this screenshot:
I'll break it down: req.readyState = 4, and batch.async = false.
Last time I checked 4 = 4. So blatantly (4 != 4) is false. And false && false is blatantly uber false, as true as Alice Cooper covering Barbie Girl.
So seeing firebug step through if (false) and onto the return statement made about as much sense as trying to raise Schrodinger's cat in a séance.
I think it's another quirk in Firebug. This time it's simply something funky going on with "step over".
The moral is: Firebug sometimes lies to you about where the current line is.
This is all part of me adapting DWR so that it can be used as a connector between Jaxer and some Java server. More on that in a bit.