I think the message should be clear in our main page. Since I'm not an
English speaker, I hope you will get the idea:

Firebird is free to use anywhere (at your house, your home-office, your
enterprise, a government agency, etc.)

However, to keep this project running we need help from people that make
profit from Firebird to join the FF or make ad-hoc donations, to ensure FB
will continue evolving.

C.