I've been through this exercise with similar requirements (an open
source CMS that has proper Firebird support, and a rich assortment of
plug-ins, modules, capabilities, etc.). I have gone through Drupal,
Wordpress, and just recently ExpressionEngine (which I have to say is
the best of breed from what I've seen so far).

However in all cases, no Firebird. I think it might also be very hard
to try and get Firebird in there. The problem isn't so much that the
CMS wouldn't be able to support other databases. The problem is that
the power of the CMS is really about not only what it brings to the
table in terms of removing a lot of general PHP coding you'd have to do
yourself, but what 3rd party add-ons are available for it. Trying to
use most of these without add-on support would end up with a pretty
simplistic CMS.

Those add-on developers really don't recognize any other database than
MySQL, and consequently 'assume' it to be the DB of choice for the CMS.
And with most CMS products being acutely aware of security
vulnerabilities, you need something that you can quickly update without
issues as a 0-Day exploit is discovered in the wild.

So in order to achieve the goal of using someone else's code for this,
and avoiding writing your own, you have to give up a lot of flexibility.
From my perspective it comes down to the requirements vs. what you
have to give up to produce something that meets the requirements. I
hate to sound like a negative engineer here, but I've not yet found a
CMS that can do what I need it to do, and certainly not with Firebird.
I ended up developing the skeleton of what I need myself with
CodeIgniter and even then I had to butcher the CI codebase to get it to
play nice with Firebird. Unfortunately its not really something that
could be used by others, but there are probably lots of 'Blog modules'
in other MVC frameworks that could be brought to bear on your project.
But you'll have to do all the heavy lifting yourself in regards to the
CMS and you'll be spending a lot of time re-inventing the wheel.

However you'll end up with what you want. Just an expensive (in terms
of time) way to get there.

Myles
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Myles Wakeham
Director of Engineering
Tech Solutions USA, Inc.
www.techsolusa.com
Phone +1-480-451-7440