Not only that, but Mozilla provides all the hooks you can imagine that let you manipulate the browser anyway you want. For example, I can write in my extension the ability to select text on the screen and search my site based on it. That's just scratching the surface, the possibilities are pretty big.
Sound like the makings of a new operating system? Makes you wonder how much longer until the browser is the first and last app you ever open. I can't wait!