DOMContentLoaded + XHR hang (tickets #1640, 1704)

I filed a bug against mozilla:
http://bugzilla.mozilla.org/show_bug.cgi?id=358387 and got some info
from their developers.

The good news: apparently the bug is fixed on the trunk with a rewrite
of the thread manager.

The bad news: we won't see today's trunk code make it into a release
until Firefox 3.0 (mid-2007 at best)

So, we may have to live with our workaround(s) for a while. (How bad
is this?)  Retrofitting the new thread manager seems very unlikely.
We could lobby for some other patch to solve the problem, but we may
have to come up with the patch ourselves...

And given that we may be in this for the long haul, do we need to
consider turning on the workaround by default in FF?

-Adam