> Can anybody explain or point to a document which describes how to configure
> JayBird and Firebird without setting any environment variables?

http://jaybirdwiki.firebirdsql.org/jaybird/doku.php?id=config:driver_config

Seems that you're trying to use either embedded server or local (IPC)
connections to Firebird. If that is not what you want to do, you used
wrong JDBC URL (see wiki page).

If that's correct, then you also have to put fbclient.dll or fbembed.dll
into the path. If that was done as well, then, very likely, you have
issues with the Firebird client library or embedded server itself
(library dependencies, config files). In this case you should check your
Firebird config first, e.g. with isql.

Roman