iPox Remix has been updated for Firefox 3.
iPox Remix is a set of tutorials on creating your own Firefox theme. You are provided with a starter theme that contains all the necessary files and images to get you going. It also contains a set of tutorials to help you customize the files and create your own theme.
Unfortunately I don’t have a tutorial for converting themes from Firefox 2 to 3. I did it manually and re-coded everything. It’s what worked best for me.