title: How to set user agent in GeckoFX?
body: <p>After using the webbrowser control for some time, I decided to give gecko a try, because of the webbrowser's problems that I've experienced, low speed and degrading performance. I downloaded the latest version of geckofx (16.0.0.2) and xulrunner(16.0.2) and created a geckoWebbrowser control. When I tried to navigate to a webpage I got a javascript.alert that my web browser is not supported and that I should use firefox>2.0.0.2 which of course is ridiculous. 
  The problem was - I assume - that the detected useragent string was "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko/ /16.0" instead of the normal firefox string "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/20100101 Firefox/18.0". '20100101' and 'Firefox' are missing from the control's useragent string. Is there any way to change it using C#? 
  I use C# winforms .net 4.5.</p>