I am not sure with the three license models of Firebird.

First citation: "New code modules added to Firebird are licensed under
the Initial Developer's Public License. (IDPL). The original modules
released by Inprise are licensed under the InterBase Public License
v.1.0. Both licences are modified versions of the Mozilla Public
License v.1.1."

My special case is:
What I understood so far is, that we can use Firebird for our office
to develop our product in this way of "commercial use".
But we sell a 3-tier-architecture j2ee software product, which needs a
rdbms as backend. We would glad to offer the customer to install at
their company the complete appserver (jboss) and rdbms (firebird),
that they can use it for no pricing. Is this allowed with the
underlying licenses? I didn't got it.

Kind regards,
Oliver Wolff