http.cookiejar.MozillaCookieJar only reads from cookies.txt, a format that Mozilla hasn't used in over a decade. It should read the file mozilla actually uses, cookies.sqlite.

Here's some code that works to turn cookies.sqlite into cookies.txt in order to read it in to MozillaCookieJar:
 http://blog.mithis.net/archives/python/90-firefox3-cookies-in-python

This was requested in 2008 in issue 2277, around the time Mozilla made the switch. The issue was rejected back then because it was too late to make the final beta for Python 2.6/3.0. I'd like to bring it up again now.

I can write a patch (since a real fix should read the cookies into the cookiejar directly, not use StringIO to create an intermediate cookies.txt) if there's any chance it would be accepted.