Capybara - visit() not working with firefox - firefox

Question

I'm a noob in cucumber and capybara, so please bear with me.
I'm trying to setup a cucumber project that uses chrome and firefox as the test platform. So far, I have got the test to work on chrome, but not on firefox.
Below is the code snippet:
require 'uri'
require 'net/http'
require 'fileutils'
require 'selenium-webdriver'
require File.dirname(__FILE__) + '/throttle.rb'
#CAPYBARA
require 'capybara/cucumber'
require 'capybara/session'
#require 'capybara-webkit'
Capybara.register_driver :chrome do |app|
Capybara::Selenium::Driver.new(app, :browser => :chrome)
end
Capybara.register_driver :selenium_firefox do |app|
Capybara::Selenium::Driver.new(app, :browser => :firefox)
end
driver = case ENV['BROWSER']
when 'chrome'
:chrome
when 'firefox'
:selenium_firefox
when 'webkit'
:webkit
when 'ie'
:internet_explorer
else
:chrome
end
Capybara.default_driver = driver
Capybara.javascript_driver = :selenium_firefox
Capybara.run_server = false
Capybara.default_selector = :css
Then, for the test, I just simply did a visit("http://www.google.com").
If I set my browser parameter to chrome, it worked fine. Cucumber openned up chrome and automatically typed in "www.google.com", and the page loaded without a problem.
However, the moment I set it to firefox: $cucumber features/test.feature BROWSER=firefox, it didn't work. It did open up the firefox browser, but nothing was being automatically typed into the URL box.
So, I must be missing something in the setup process that I'm not aware of. I have been looking for solutions on the web (require 'selenium webdriver', put 'selenium webdriver' into my Gemfiles, etc.), but so far none has worked for me.
What am I missing here? How come visit() didn't automatically populate the URL box of firefox, but it did just fine with chrome?
Thank you for your help.