Java plugin easily crashed if the user changed mozilla's useragent string to something else other than the default one. More detail please see:

https://bugzilla.mozilla.org/show_bug.cgi?id=83376

Since the java plugin libraries have already been loaded into memory, java plugin should be able to know which version of browser it is working with. No need borthering to parse the useragent string to get such information.
###@###.### 2004-12-29 09:10:20 GMT