Hi

If every user has root access (linux) or admin access (windows), there isn't
much you can do.
BUT if you have at least normal user accounts for the users, simply give
only firebird access to the file.
A user who cannot access the database file, cannot copy it.

If you are concirned about users tracing your network traffic and therefor
getting you firebird password, then you could encrypt that traffic using ssh
or zebedee (both for windows and linux available).

This will leave as the only place for attacks the client and server computer
itself. Some network spy software could intercept network communication
between ssh/zebedee and firebird server/client. But usually users should not
be able to run third party software without you knowledga on these systems.

Regards,
Steffen