You can actually use either element as the root of your doc. Use the firebird-ds.xml as the example since the generic-ds.xml only shows stuff for a jca-jdbc wrapper, whereas the firebird-ds.xml shows deploying a standalone jca connector.
Use the attached *-ds.xml as a guide.
It works for me.
Also, look @ JCAConfig.pdf doc released recently
on Sourceforge site -
http://sourceforge.net/projects/jboss/. It has
pointers on configuration.
Let us know if you have any questions.