Here's an update to my exploration with php, php-gtk, adodb and firebird:

Basically I got drawn into using Firebird as a backend because of a particular software need (which required Firebird) and that remains unchanged. PHP was also involved because it seemed to have strong support for Firebird (via php_interbase). And php-gtk came into the picture because of the need for a good gui front-end to the application I'm developing (a shell for a remote accounting application).

Well, as I noted earlier, PHP-GTK was lagging in development support, so the idea of an open-source gui development environment kind of went with that. I then found PyGTK to be much more up to speed with developments in the GTK+ and Glade world and played with them, in conjunction with Python. My only concern was how well it'd support Firebird.

Well, turns out Python has great support for Firebird, including a superb extension called SQLAlchemy. SQLAlchemy combines data abstraction layering with object relation mapping, and ends up providing a near seamless combination of OOP design (classes on the front end) while adhering to good RDBMS data normalization design on the back end. It works really well and is something well worth checking out.

So, after much experimentation, I'm off on the Python trail (along with Firebird). : )