class Selenium::WebDriver::Firefox::Profile

def update_user_prefs_in(directory)
  path = File.join(directory, 'user.js')
  prefs = read_user_prefs(path)
  prefs.merge! self.class::DEFAULT_PREFERENCES
  prefs.merge!(@additional_prefs)
  # If the user sets the home page, we should also start up there
  prefs['startup.homepage_welcome_url'] ||= prefs['browser.startup.homepage']
  write_prefs prefs, path
end