Adblock
From MozillaZine Knowledge Base
Adblock is an extension for Firefox and the Mozilla Suite. It can hide graphics on pages, block them from ever loading, block JavaScript files, embedded frames (IFRAMEs), and Flash movies.
Adblock Plus a forked version that is recommended on Mozilla Add-ons and consistently one of the five most downloaded Firefox extensions. It supports filter subscriptions or you can write your own filters.