I'm trying to run Selenium's Firefox webdriver and am getting the error below. I can see that the response does not have a sessionId - the offending line is self.session_id = response['sessionId'] - but I don't know why. I've run this in the following ways and get the same error: 

Cygwin, running nosetests 
Cygwin directly
Windows, running nosetests
Windows directly


    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "C:\dev\tools\cygwin\home\207013288\dev\projects\scorpion\test\unit\test_
    approve_workflows.py", line 27, in test_login
        'password', userid='207013288', test=True)
      File "C:\dev\tools\cygwin\home\207013288\dev\projects\scorpion\src\workflows.p
    y", line 20, in login
        browser = webdriver.Firefox()
      File "C:\dev\sdks\Python33\lib\site-packages\selenium-2.32.0-py3.3.egg\seleniu
    m\webdriver\firefox\webdriver.py", line 62, in __init__
        desired_capabilities=capabilities)
      File "C:\dev\sdks\Python33\lib\site-packages\selenium-2.32.0-py3.3.egg\seleniu
    m\webdriver\remote\webdriver.py", line 72, in __init__
        self.start_session(desired_capabilities, browser_profile)
      File "C:\dev\sdks\Python33\lib\site-packages\selenium-2.32.0-py3.3.egg\seleniu
    m\webdriver\remote\webdriver.py", line 116, in start_session
        self.session_id = response['sessionId']
    nose.proxy.KeyError: 'sessionId'
    -------------------- >> begin captured logging << --------------------
    selenium.webdriver.remote.remote_connection: DEBUG: POST http://127.0.0.1:63801/
    hub/session {"sessionId": null, "desiredCapabilities": {"version": "", "browserN
    ame": "firefox", "platform": "ANY", "javascriptEnabled": true}}
    --------------------- >> end captured logging << ---------------------

I haven't used Selenium before and I'm not sure where to go from here.
MAC OSX SOLUTION
I'm using Python 2.7 and FireFox 48.0.2 and Chrome Versie 57.0.2987.98 (64-bit).
The error *self.session_id = response['sessionId']* for me was solved by going to System preferences -> Network -> Advanced in the Wifi Tab. -> Proxy's -> Turning "Automatic Proxydetection" on. 
After changing this, the error no longer occurred.
Why doesn't Selenium's response have a sessionId?