From Bugzilla Helper:   
User-Agent: Mozilla/5.0 (compatible; Konqueror/3.0.0-10; Linux)   
   
Description of problem:   
http://fhbonline.fhb.com   
In order to connect to this online banking website, I must make my web browser   
user agent "Mozilla/4.0 (compatible; MSIE5.5; Windows NT 5.0".  My local LUG   
is working toward pushing the bank to fix their website, but in the mean time   
that user agent exposed a bug in Mozilla.   
   
If the following line is added to the Mozilla prefs.js, Mozilla fails to run.   
user_pref("general.useragent.override", "Mozilla/4.0 (compatible; MSIE5.5;   
Windows NT 5.0");   
   
At first it seems to fail quietly without an error message, but if you run 
"mozilla -splash" you see the actual error message  
  
INTERNAL ERROR on Browser End: Expected a version > 5! Version = 4  
  
System error?:: Success  
   
Version-Release number of selected component (if applicable):   
Red Hat Linux 7.3 
mozilla-0.9.9-12.7.3 
   
How reproducible:   
Always 
    
Steps to Reproduce:   
1. Add user_pref("general.useragent.override", "Mozilla/4.0 (compatible; 
MSIE5.5; Windows NT 5.0");  to your prefs.js. 
2. Attempt to start Mozilla.