That's exactly how I do it using Firefox on my Ubuntu 13.04 workstation. I see nothing wrong in your explanation.
Are you trying to access it from the same computer that the development server is running on?
If so, then check to see whether you have a firewall running on your workstation which may be blocking port 8000.
If you are trying to see it from another computer, then your server needs to listen on other ports. Try "python manage.py runserver
0.0.0.0:8000"
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Vernon