I am creating some end-to-end tests for a web app using Selenium.
I am working in Python and using the Firefox driver
driver = webdriver.Firefox()
I believe the default is to launch Firefox with a new, anonymous profile. You can launch selenium with -Dwebdriver.firefox.profile=whatever, where "whatever" is the name of a profile when you launch firefox -P.
To make sure there's no weirdness with persistent logins and other cookies: