In the Privacy User-Prefs, an option is given to identify as Netscape 6. The string is not correct. The important 'Gecko' part is missing. See:
http://developer.netscape.com/evangelism/docs/articles/find-gecko/
I suggest:
"Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:0.9.4) Gecko/20011128 Netscape6/6.2.1"