PS: I think this is the reason for regression
If your JS code is linked in via a <script> element, then by the time that
<script> executes, all the stylesheets that had started loading before the
parser got to that <script> will be loaded.
The point of the change in bug 84582 was to not have sites try to answer that
Now for the site in question
(http://extjs.com/deploy/dev/examples/desktop/desktop.html), the <link> for the
last stylesheet comes _after_ all the scripts. So it's possible for some events
(especially DOMContentLoaded) to execute before the stylesheet loads. I'm not
going to dig through those scripts right now, but that's my best guess for
what's going on: the site is running code that wants layout information from
DOMContentLoaded instead of onload...
OK follow up question... how about if the stylesheets themselves have
@import statements to recursively load other stylesheets?
A sheet is not considered to have loaded until all sheets it @imports have loaded.