title: unable to call firefox from selenium in python on AWS machine
body: <p>I am trying to use selenium from python to scrape some dynamics pages with javascript. However, I cannot call firefox after I followed the instruction of selenium on the pypi page(http://pypi.python.org/pypi/selenium). I installed firefox on AWS ubuntu 12.04. The error message I got is:</p>
  
  <pre><code>In [1]: from selenium import webdriver
  
  In [2]: br = webdriver.Firefox()
  ---------------------------------------------------------------------------
  WebDriverException                        Traceback (most recent call last)
  /home/ubuntu/&lt;ipython-input-2-d6a5d754ea44&gt; in &lt;module&gt;()
  ----&gt; 1 br = webdriver.Firefox()
  
  /usr/local/lib/python2.7/dist-packages/selenium/webdriver/firefox/webdriver.pyc in __init__(self, firefox_profile, firefox_binary, timeout)
       49         RemoteWebDriver.__init__(self,
       50             command_executor=ExtensionConnection("127.0.0.1", self.profile,
  ---&gt; 51             self.binary, timeout),
       52             desired_capabilities=DesiredCapabilities.FIREFOX)
       53
  
  /usr/local/lib/python2.7/dist-packages/selenium/webdriver/firefox/extension_connection.pyc in __init__(self, host, firefox_profile, firefox_binary, timeout)
       45         self.profile.add_extension()
       46
  ---&gt; 47         self.binary.launch_browser(self.profile)
       48         _URL = "http://%s:%d/hub" % (HOST, PORT)
       49         RemoteConnection.__init__(
  
  /usr/local/lib/python2.7/dist-packages/selenium/webdriver/firefox/firefox_binary.pyc in launch_browser(self, profile)
       42
       43         self._start_from_profile_path(self.profile.path)
  ---&gt; 44         self._wait_until_connectable()
       45
       46     def kill(self):
  
  /usr/local/lib/python2.7/dist-packages/selenium/webdriver/firefox/firefox_binary.pyc in _wait_until_connectable(self)
       79                 raise WebDriverException("The browser appears to have exited "
       80                       "before we could connect. The output was: %s" %
  ---&gt; 81                       self._get_firefox_output())
       82             if count == 30:
       83                 self.kill()
  
  WebDriverException: Message: 'The browser appears to have exited before we could connect. The output was: Error: no display specified\n'
  </code></pre>
  
  <p>I did search on the web and found that this problem happened with other people (https://groups.google.com/forum/?fromgroups=#!topic/selenium-users/21sJrOJULZY). But I don't understand the solution, if it is. </p>
  
  <p>Can anyone help me please? Thanks!</p>