Cool Firefox Add-ons.

[Hackfest]

Here's are a couple of my personal favorites:

Adblock + blocks most ads automatically, but you can right click any pic, banner, ad, etc. Plus, when you choose "adblock frame" it bumps the normal page up. For instance, on this page it takes away the box at the top of the page completely.
adblockplus.org/en/

Flashblock blocks flashplayer ads, which are becoming more and more common.
www.techiecorner.com/90/block-flash-and-speed-up-page-load-with-flash-block-firefox-extension/

Let's all add some of our favorites.

[Kizzume]

One that I use as well is called NoScript. It blocks all javascript except from places you specify. A lot of flash ads and spyware get installed through those means, so blocking those things except the ones you specify is a nice way to do it. The context menu is really easy to use.

Here's the direct download link
addons.mozilla.org/en-US/firefox/downloads/file/19307/noscript-1.1.7.2-fx+mz+sm+fl.xpi

And here's the info page
addons.mozilla.org/en-US/firefox/addon/722