Selenium, how to start Firefox with addons?

I want to load the Firefox Addon RequestPolicy. This is how i tried it:

rp = open(wd + "/requestpolicy.xpi")
firefoxProfile = FirefoxProfile()
firefoxProfile.add_extension(rp)

self.driver = webdriver.Firefox(firefoxProfile)

self.usr = user.User(self.driver, username, password, world)
self.usr.login()

No error, according to the Docs it should work, but it doesn't, it still starts without the addon.

Next thing i've tried is calling it this way:

self.driver = webdriver.Firefox(browser_profile=firefoxProfile)

Output:

TypeError: __init__() got an unexpected keyword argument 'browser_profile'

But this is an aspect of python i dont know much about. I got that idea because the source looks that way.