Jess,
that's the odd thing - no changes were made to WIndchill or Creo and one day that config line starts causing problems. As a matter of fact, it just happened again on a workstation which was running the config file with the mozilla bowser type option just fine - then today Creo stalled after login. Removing the browser type option from the config file once again fixed the issue.
Unless all these users (3 total now) are somehow messing up their 'Gecko' libraries on their systems, I can't explain why this config option suddenly causes problems.
Andri