Description of problem:

When a popup window is created by firefox, firefox often goes into some kind of
unresponsive hang state for a few seconds.

Version-Release number of selected component (if applicable):

1.5-0.5.0.rc1

How reproducible:

Most of the time. I can't seem to get firefox to do it right now though, but it
did happen a few minutes ago on the same firefox instance.

Steps to Reproduce:
1. Open firefox
2. Type control-d or control-i
  
Actual results:

Firefox becomes unresponsive for a few seconds

Expected results:

Firefox should be responsive even while popup windows are opening.