In Conkeror, when visiting:

  http://www.newzbin.com

You'll notice the login table is rendered in quirks mode, to verify: 
  - open DOM inspector
  - inspect the "Account Login" box
  - inspect the "TABLE"
  - view it's CSS style rules
  - notice "resource://gre/res/quirk.css" is loaded/applied

If you perform the same task in Firefox, you'll notice that quirks mode is not applied. 

In case it's of importance, I am running:
   firefox 3.0.10
   xulrunner 1.9.0.10
   conkeror (compiled from 2009-04-24)

Note that this also happens on http://reader.google.com, but the newzbin login page is a much simpler
page to analyze.

Just more info about this, it appears that opening a buffer to one of these pages in the background will
cause it load correctly. When browsed to normally, quirk.css will be applied to at least table elements.

Don't know what the difference between conkeror and firefox is still, but it's a bug from xulrunner. For
more information see:

   https://bugzilla.mozilla.org/show_bug.cgi?id=450191

To fix it you must apply the provided patch (with some tweaking if you're going to use the latest stable
instead of the alpha releases).

Thanks for your diligence!

According to the bugzilla report, the issue was fixed in XULRunner 1.9.1, which is now Conkeror's
minimum XULRunner requirement, so closing ticket.