Confirming access to alerts in a StackOverflow question

gistfile1.rb

#!/bin/env ruby
# encoding: utf-8

# Trying to replicate error described in a StackOverflow Question
# http://stackoverflow.com/questions/31065711/watir-webdriver-does-not-show-dialogs-in-firefox-when-finished-testing

require 'os'
require 'headless'
require 'watir-webdriver'

def click_on_button(b)
  b.goto "http://www.w3schools.com/js/tryit.asp?filename=tryjs_alert"

  frame_container = b.div(:class => "container").div(:class => "iframecontainer")
  iframe = frame_container.div(:class => "iframewrapper").iframe(:id => "iframeResult")
  iframe.button(:onclick => "myFunction()").click

  result = true if b.alert.exists?

  b.alert.close if b.alert.exists?

  return [result, b]
end

begin
  h = Headless.new if OS.linux?
  h.start if h
  b = Watir::Browser.new :firefox

  results = click_on_button(b)
  success = results[0]
  b = results[1]

  raise 'Unable to find alert on the first pass.' unless success

  sleep(5)

  click_on_button(b)
  success = results[0]

  raise 'Unable to find alert on the second pass.' unless success
ensure
  h.destroy_sync if h
  b.close if b
end

# => No errors raised.
# => FF 38, selenium-webdriver (2.46.2), watir-webdriver (0.7.0)