How to find browser user-agent with selenium in ruby

I want to know current user-agent. I have used selenium2 with ruby

I have set user-agent in env.rb

  Capybara.default_driver = :selenium
  Capybara.register_driver :selenium do |app|

  profile = Selenium::WebDriver::Firefox::Profile.new
  profile['general.useragent.override'] = "Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_0 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A293 Safari/6531.22.7"

  Capybara::Selenium::Driver.new(app, {:browser => :firefox, :profile =>  profile})
end

And when run cucumber test cases opened FireFox Browser and I does not see iphone. SO I want to check test cases is running in with iphone mode(user-agent). How can I do that?