How can you detect the version of a browser?

Question

I\'ve been searching around for code that would let me detect if the user visiting the website has Firefox 3 or 4. All I have found is code to detect the type of browser but

Answer 1

var ua = navigator.userAgent;

if (/Firefox\//.test(ua))
   var Firefox = /Firefox\/([0-9\.A-z]+)/.exec(ua)[1];