via oreilly.de :
"Firefox Hacks is ideal for power users who want to maximize the effectiveness of Firefox, the next-generation web browser that is quickly gaining in popularity. This highly-focused book offers all the valuable tips and tools you need to enjoy a superior and safer browsing experience. Learn how to customize its deployment, appearance, features, and functionality."

Samples:
Hack 27: Fix Web Servers to Support Firefox Content
Hack 31: Take Firefox with You
Hack 43: Waste Time with Toys and Games
Hack 44: Tweak and Troubleshoot CSS Designs
Hack 69: Make New Tags and Widgets with XBL
Hack 92: Get a Custom, Prebuilt Version
Read the sample chapters here