This is not a book review or anything, but i am referring to the above book at oreilly.com. You can find a detailed review at slashdot. What i am posting about is one of the sample chapters. If you are a techie firefox user with an interest in XML, HTML, Firefox and related stuff then you may want to check out hack 69 - Make new tags and widgets with XBL.
XBL (Extensible Binding Language) is one of mozilla project which is being slowly adopted by W3C. For the interested one, you might also want to check out an introduction to XBL on XULPlanet.com.