What Navajoa said.
Firefox is great for its diversity of really useful add-ins. At the moment I'm forced to use a laptop where I don't have admin status, so I can't install it and therefore I have to make-do with an ancient version of Explorer. And yes, the ads are driving me spare!
As soon as I have my own functioning computer again I'll be going straight back to Firefox and blocking these and other ads.
It'll save on download limits too, and it speeds things up. Well worth the effort.