我有以下脚本

from selenium import webdriver

browser = webdriver.Firefox()
browser.get('http://localhost:8000')

assert 'Django' in browser.title

我收到以下错误

$ python3 functional_tests.py 
Traceback (most recent call last):   File "functional_tests.py", line 3, in <module>
    browser = webdriver.Firefox()   File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/firefox/webdriver.py", line 80, in __init__
    self.binary, timeout)   File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/firefox/extension_connection.py", line 52, in __init__
    self.binary.launch_browser(self.profile, timeout=timeout)   File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/firefox/firefox_binary.py", line 68, in launch_browser
    self._wait_until_connectable(timeout=timeout)   File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/firefox/firefox_binary.py", line 99, in _wait_until_connectable
    "The browser appears to have exited " selenium.common.exceptions.WebDriverException: Message: The browser appears to have exited before we could connect. If you specified a log_file in the FirefoxBinary constructor, check it for details.

pip3 list显示selenium (2.53.6)。

firefox -v显示Mozilla Firefox 47.0。