"Limited ODBC" means that powerbuilder does not include certain ODBC
drivers in the installation. But, native support for Firebird? Been
working 5 years with that combination (firebird + powerbuilder) and
there is not such thing (as far i know) even in professional or
enterprise wich i use.

Try Firebird ODBC, it's open source, and works great.

You can also try Powerbuilder Desktop 10. Starting from 10, there is
no more Professional Edition, just desktop and enterprise.

Difference between both? Just web capabilities and perhaps other
things like DOM and XML, web services, etc.