I've stumbled across another sweet Firefox extension after listening to the FLOSS Weekly podcast with Ben Goodger of Firefox. One of the guys on the show mentioned an extension called Flashblock. It blocks all of those annoying Flash ads. If you decide you actually want to see whatever Flash has been blocked, all you have to do is click it.
I've been wishing there was an Adblock equivalent for Flash. Guess I should've looked harder.
I downloaded it here. It's also on Mozilla's Firefox Add-ons site.