[William](http://wpram.com/) has made an excellent [introduction to Firefox](http://wpram.com/log/2005/03/11/slideshow_introducing_firefox) in the form of slideshow. The slideshow is available in PDF format and licensed under the Creative Commons Attribution-Non Commercial License. That means you may use it for your own FireFox advocacy as long as it is non commercial and you retain any attribution to William himself.
The slideshow consisted of two parts, the first part tries to introduce FireFox to casual users, and the second part tries to introduce it to web developers. It is written in English, but he welcomes anybody who wants to make a translation.