The Firebird Book (Second Edition) is now available as a print on demand book (at createspace) in three parts,

Volume 1: Firebird Fundamentals

Volume 2: Developing with Firebird Data

Volume 3: Administering Firebird Servers and Databases

Also and also in electronic format (e-book) on the Developer DVD or as an immediate download. It covers Firebird upto Firebird V2.5.x.

Anybody purchasing the DVD gets a download link immediately,
and the DVD is sent later as a backup hard copy, along with a lot of other useful stuff.