The creation of indexes on FKs seems to be a best-practice for MS-SQL-server and ORACLE and is not needed with Firebird; in Firebird instead than a best-practice is the default behavior: the FK includes an index.
That said I have to be sure that each FK has to have an index. After check our mappings I have realized that no one of our tables have the corresponding index for each FK.
Big PITA ?… no! that has been the lucky, because now I can create a very little piece of code to let NHibernate create all needed indexes for me.
P.S. perhaps I'll be back to my blog...perhaps