http://flashblock.mozdev.org/installation.html

Flashblock is an extension for the Mozilla and Firefox browsers that takes a pessimistic approach to dealing with Macromedia Flash content on a webpage and blocks ALL Flash content from loading. It then leaves placeholders on the webpage that allow you to click to download and then view the Flash content.

Flashblock currently blocks the following content types:

Macromedia Flash
Macromedia Shockwave
Macromedia Authorware