Change UserAgent in Firefox

Hi,

need help to change in firefox useragent

My script is very simple:

   Run('"C:\Program Files\Mozilla Firefox\firefox.exe"')
   Sleep(5000)
   Send("http://www.google.com")
   Send("{ENTER}")
   Sleep(5000)

...

So,i need to open browser each time with new UserAgent

Currently i am using User Agent Switcher add for firefox and with mouse move/select manual useragent

but,i am curious if t could set useragent direct with au3 function

*NOTE: Only for Firefox