Found session description from last Firebird conference. You can
investigate that as well.

171 - Moving applications from Oracle to Firebird
Paul Ruizendall
Database indepence has proven to be an elusive goal. Almost all
realworld enterprise applications are dependent on the database
system they were designed for. This dependence ranges from
differences in data formats, to differences in SQL dialect and to
differences in lock behaviour. As a result, porting large enterprise
applications to another database is either impossible due to lack of
particular features or very costly because of the amount of code
change needed. Stored procedures are particularly hard to port.

The 'Fyracle' project delivers database indepence for large,
Oraclebased applications, by extending the open source, enterprise
class
Firebird RDBMS to accept Oracle-style SQL and PL/SQL stored
procedures. This will be demonstrated by showing how the popular
"Compiere" open source ERP+CRM package runs on Firebird -- with
virtually no change to the Compiere code base.