> In theory, if I create a Firebird database with IBExpert under
> MS-Windows, is it then possible to use it with a Linux application
> (written in Lazarus), giving it all the right rights, ie without going
> through an IBExpert's script export and re-import into FlameRobin)?
>

IBExpert, Flamerobin and your Lazarus based application call all connect
to the same server which can be running on any of your computers.

In case you are using firebird in embedded mode you cannot really share
database between different machines since it is not an good idea to
place database on an network share.