test-capybara.rb

File.open("test.html", "w") { |file| file << "<h1>hello</h1>" }
url = "file://#{File.expand_path '../test.html', __FILE__}"

require 'capybara'
browser = Capybara::Session.new(:selenium)
browser.visit url
puts browser.find("h1").text

test-selenium.rb

File.open("test.html", "w") { |file| file << "<h1>hello</h1>" }
url = "file://#{File.expand_path '../test.html', __FILE__}"

require 'selenium-webdriver'
browser = Selenium::WebDriver.for :firefox
begin
  browser.get url
  puts browser.find_element(:tag_name => "h1").text
ensure
  browser.quit
end

The test-capybara script fails with Capybara 1.1.2 (on my machine at least) but it does pass on Capybara 2.0.0 beta2.