rubygem-selenium-webdriver-2.38.0 doesn't work with firefox

[absolutelyconvergent at gmail.com]

#!/usr/local/bin/ruby
require 'rubygems'
require 'selenium-webdriver'
driver = Selenium::WebDriver.for :firefox
driver.get "http://example.com/"
puts "Page title is #{driver.title}"
driver.quit

This simple script finished with a popup message, saying Profile missing: Your 
Firefox profile cannot be loaded. It may be missing or inaccessible.
And no luck with Selenium::WebDriver::Firefox::Profile.from_name.

But py27-selenium-2.42.0 worked fine.