[Tutor] selenium programs stopped working

[Benjamin Fishbein]

I'm using selenium webdriver with python 2.7. I have some programs I wrote with it and they've been working properly for some months.
But today I tried to write a new program with the selenium module.

from selenium import webdriver
from selenium.webdriver.common.keys import Keys

driver = webdriver.Firefox()
driver.get("http://www.python.org") # actually I go to other sites, not python.org
# now there's more but the program never gets to it

The Firefox web browser opens, but it doesn't go to any page. The url doesn't even appear in the box at the top of the webbrowser where urls go.
Do you know what is causing this problem? The only thing I can think of is that there's some problem in the settings. I shut down the computer and turned it back on, but the problem remains.
Any help would be greatly appreciated.
Thanks,
Ben