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

Volume 1: Firebird Fundamentals

https://www.createspace.com/4203352

Volume 2: Developing with Firebird Data

https://www.createspace.com/4206843

Volume 3: Administering Firebird Servers and Databases

https://www.createspace.com/4206991

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.