Description of problem:
When first run (per profile) FF4 exits with an html dialog:
  XML Parsing Error: undefined entity
  Location: chrome://mozapps/content/extensions/update.xul
  Line Number 14, Column 1:<wizard id="updateWizard"
  ^
On successive runs, FF4 exits immediately after the profile dialog, with no error.

Version-Release number of selected component (if applicable):
firefox4-4.0-0.12.b10.fc14.x86_64
xulrunner2-2.0-0.11.b10.fc14.x86_64
(current update. problems occured in previous version, too)

How reproducible:
every time

Steps to Reproduce:
1. Launch FF4
2. Select Profile
  
Actual results:
Dialog box, exit.

Expected results:
Normal window.

Additional info:
FF4 ran fine for a couple of weeks. Then it stopped normal execution (I'm not certain if there was an update to something at the time.)

Upon searching, found that it was complaining about "cannot read application.ini". Found Bug 664877. Followed the instructions to:
  cp /usr/lib64/firefox-4/application.ini /usr/lib64/xulrunner-2/ 
Which fixed the application.ini error. At that point, existing profiles would just terminate upon launching. Attempted to create a new profile for testing, and noticed that the first run of any profile gave this 'updateWizard' error.

That bug indicates that people started getting the bug after removing the .mozilla directory. I have not done so. I was running fine, trying out ff4 every few days, and one day it stopped working.

Have both ff and ff4 on this machine. They both seem to share the same profiles, so I've only been running them alternately. Attempted to separate them by creating an ff4-only profile, which changed nothing. Attempted to separate them further by creating a new user account, and running ff4 in that account, via su. This works (leading me to think something is hosed in the profile, but I don't know what).

The two accounts behave differently. In particular, if I remove the /usr.lib64/xulrunner-2/application.ini file, my main account complains that it is missing; but the account I created for ff4 doesn't seem to notice the difference.

I am attempting to launch ff4 in my normal account in safemode.