User Agent String.Com 

User Agent String explained :

Firefox 3.5.8
Mozilla	MozillaProductToken. It's a Mozilla based user agent
5.0	Mozilla Version
X11	X Window System a windowing system for bitmap displays
U	Security values: N for no security U for strong security I for weak security
FreeBSD i386	Operating System: FreeBSD running on a Intel 80386 CPU
ja-JP	Language Tag, indicates the language for which the client had been localized (e.g. menus and buttons in the user interface) ja-JP = Japanese - Japan
rv:1.9.1.8	CVS Branch Tag The version of Gecko being used in the browser
Gecko	Gecko engine inside
20100305	Build Date: the date the browser was built
Firefox	Name : Firefox
3.5.8	Version
First visit:	2010.03.13 08:32
Last visit:	2010.03.13 08:32
All Firefox user agent strings