User Agent String.Com 

User Agent String explained :

Firefox 1.0.1
Mozilla	MozillaProductSlice. Claims to be a Mozilla based user agent, which is only true for Gecko browsers like Firefox and Netscape. For all other user agents it means 'Mozilla-compatible'. In modern browsers, this is only used for historical reasons. It has no real meaning anymore
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
Linux i686	Operating System: Linux running on a Intel Pentium Pro CPU
en-US	Language Tag, indicates the language for which the client had been localized (e.g. menus and buttons in the user interface) en-US = English - United States
rv:1.7.6	CVS Branch Tag The version of Gecko being used in the browser
Gecko	Gecko engine inside
20050310	Build Date: the date the browser was built
Firefox	Name : Firefox
1.0.1	Firefox version
Last visit:	2018.07.29 10:00
All Firefox user agent strings