Don't know if this will help, but there are two things I seem to do
slightly differently:

instead of
Class.forName("org.firebirdsql.jdbc.FBDriver").newInstance();
I use:
Class.forName (FBDriver.class.getName ());


While you do not "yet" have a problem with:
String url = "jdbc:firebirdsql://trans//dbs/test.gdb";
I think you might, my code looks more like:
String url = "jdbc:firebirdsql://trans/3050:dbs/test.gdb";
assuming trans is the server and 3050 is the port firebird is listening
to.


The type 4 driver does work, good luck in getting it working in your
environment

Bill