Adblock Plus is one Firefox extension that may be a good enough reason on it’s own to start using Firefox if you’re not already. As the name implies, it blocks every advertisement from nearly every site on the web and does a damn good job of it too. After installing the basic extension, you then “subscribe” to a huge list of known file extensions for advertisements. You also have the option of creating your own list of ads you want to block as you surf. After using it for sometime, sites I usually visit are unbearable to look at without it.
I have heard some debate about the morals of using Ad Block Plus since it can cut into the revenue stream of websites that rely primarily on advertisements, but ultimately it’s your decision.
Ad Block Plus can be found here.