我正在试验Firefox的WebDriver，请问是否可以处理“下载”窗口（接受或拒绝传入的下载请求）？

例如，一段简单的代码：

import selenium.firefox.webdriver

dr = selenium.firefox.webdriver.WebDriver()
# Firefox is showed up.

# Let's say I'd want to download python.
dr.get('http://python.org/ftp/python/3.1.3/python-3.1.3.msi')
# Download window is showed up.
# How could I accept the download request?

# As I understand, the method below should return 
# two handles but I get only main window's handle. 
handles = dr.get_window_handles()

# Seems like WebDriver cannot "see" this popup.

我已经对此进行了一些尝试，但是还没有找到解决方案。我真的很感谢任何提示。

非常感谢，-V