And for those of you who are wanting to tell me "but Firefox just joins all startups into the same process and only gives you a new window". Well, I defeated that by dynamically creating a new home directory on the fly for each startup, populating it with a template set of files Firefox expects, setting the HOME environment variable to that path, and starting the Firefox process. So the scanning of my browser is limited to just what this one I use for Slashdot has visited recently.
If you didn't want to go through all of that hassle, you could have just done:
env MOZ_NO_REMOTE=1 firefox --ProfileManager
It starts a new firefox instance and gives you the option of creating a new profile for a site. Comes in handy for me.
Also check out prism
Recent investments will yield a slight profit.