title: Selenium WebDriver can't find Firefox when installed with Homebrew cask
body: <p><code>Homebrew</code> cask does some app linking magic on Mac OS X. Apparently it's not good enough because Selenium WebDriver looking for the Firefox executable can't find it. The following is an error message from an <code>RSpec</code> test run with <code>Capybara</code> driving Selenium.</p>
  
  <p>What is a good way to hint the location of the Firefox executable?</p>
  
  <pre><code>Failure/Error: Unable to find matching line from backtrace
   Selenium::WebDriver::Error::WebDriverError:
     Could not find Firefox binary (os=macosx). Make sure Firefox is installed or set the path manually with Selenium::WebDriver::Firefox::Binary.path=
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/binary.rb:127:in `path'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/binary.rb:60:in `execute'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/binary.rb:34:in `start_with'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/launcher.rb:70:in `start_silent_and_wait'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/launcher.rb:35:in `block in launch'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/socket_lock.rb:20:in `locked'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/launcher.rb:32:in `launch'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/firefox/bridge.rb:24:in `initialize'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/common/driver.rb:31:in `new'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver/common/driver.rb:31:in `for'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/selenium-webdriver-2.43.0/lib/selenium/webdriver.rb:67:in `for'
   # /Users/mende/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/capybara-2.4.4/lib/capybara/selenium/driver.rb:13:in `browser'
  </code></pre>