Why promote Firefox? If you're using it already, then there's no reason to not tell everyone!
Why are you using it instead of a default installed browser.
How can I promote Firefox easily?
Word of mouth is the best source usually, but there's no harm is showing your dedication/enthusiasm with graphic badges on your site, blog, profile pages, etc.
Where can I track or get credit for refering Firefox
To show your Firefox love, and get credit for it, go signup at www.spreadfirefox.com, and get the your referal link/ID, and spread it around like it's free money!
Cool, are there graphics (buttons, banner) freely available?
You can make your own, of course, but there is a handful of premade buttons that fit almost any occassion/site, and even have blank versions ready for your own message
Okay, what do I get out of "spreading the word"?
A pat on the back, and a cool button... you though there was free pie?!
Honestly, if you design sites and hate bad-browsers, then here's a small token of "doing something about it."
From Spread Firefox: Firefox is not just another piece of software. It is built by a community of volunteers passionate about maintaining innovation and choice on the web, and preserving the standards that make the Net so different from gated online communities that preceded it. Our source code is free available for anyone to inspect and hundreds of experienced developers help us make our code more secure and add the exciting new features Firefox users have come to love.