Adblock is an excellent Firefox extension but has its failings. Among my Adblock pet peeves are its lack of a whitelist and general absence of options. Adblock Plus is an extension that tries to succeed where Adblock does not. It (as of version 0.6) is a complete rewrite of Adblock that does everything its successor does but adds whitelisting, preferences to control how it behaves, and a sidebar that will show you all of the objects on a page and let you choose what to block.