title: Missing 'marionetteProtocol' field in handshake
body: <p>Not sure what's going on. It might be that I have an error because I may not have the latest version of a module or something when I run this python script. I get the following error:</p>
  
  <pre><code>WebDriverException                        Traceback (most recent call last)
  &lt;ipython-input-17-d1a8ab171ac2&gt; in &lt;module&gt;()
        3 from selenium import webdriver
        4 
  ----&gt; 5 driver = webdriver.Firefox()
        6 from selenium.webdriver.common.keys import Keys
        7 from bs4 import BeautifulSoup
  
  //anaconda/lib/python2.7/site-packages/selenium/webdriver/firefox/webdriver.pyc in __init__(self, firefox_profile, firefox_binary, timeout, capabilities, proxy, executable_path, firefox_options, log_path)
      153                 command_executor=executor,
      154                 desired_capabilities=capabilities,
  --&gt; 155                 keep_alive=True)
      156 
      157         # Selenium remote
  
  //anaconda/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.pyc in __init__(self, command_executor, desired_capabilities, browser_profile, proxy, keep_alive, file_detector)
       90         self.error_handler = ErrorHandler()
       91         self.start_client()
  ---&gt; 92         self.start_session(desired_capabilities, browser_profile)
       93         self._switch_to = SwitchTo(self)
       94         self._mobile = Mobile(self)
  
  //anaconda/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.pyc in start_session(self, desired_capabilities, browser_profile)
      177         if browser_profile:
      178             capabilities['desiredCapabilities']['firefox_profile'] = browser_profile.encoded
  --&gt; 179         response = self.execute(Command.NEW_SESSION, capabilities)
      180         if 'sessionId' not in response:
      181             response = response['value']
  
  //anaconda/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.pyc in execute(self, driver_command, params)
      236         response = self.command_executor.execute(driver_command, params)
      237         if response:
  --&gt; 238             self.error_handler.check_response(response)
      239             response['value'] = self._unwrap_value(
      240                 response.get('value', None))
  
  //anaconda/lib/python2.7/site-packages/selenium/webdriver/remote/errorhandler.pyc in check_response(self, response)
      191         elif exception_class == UnexpectedAlertPresentException and 'alert' in value:
      192             raise exception_class(message, screen, stacktrace, value['alert'].get('text'))
  --&gt; 193         raise exception_class(message, screen, stacktrace)
      194 
      195     def _value_or_default(self, obj, key, default):
  
  WebDriverException: Message: Missing 'marionetteProtocol' field in handshake
  </code></pre>