Firefox uses separate processes for code isolation, both to prevent sites from spying on one another and to reduce the ability of one failing component to take down the whole browser. I think most modern browsers work similarly. To see what those processes are being used for, you can view Firefox's ''internal'' Task Manager by pressing Shift+Esc. This will show the processes that Firefox is using for its own code, add-ons, and web pages. As for whether it is being efficient, that is hard to say. Some features/functions/sites use more resources than others.