Firefox 3.0: template using RDF in-memory-datasource

I want to display the contents of an in-memory-datasource (I'm
updating Robert Ginda's XPCOM Component Viewer for Firefox 3.0). When
starting with datasources="rdf:null", it seems the only way to get a
template to display is to set the datasources attribute. Calling
methods on tree.database (AddDataSource, refresh, rebuild) seems to
have no effect.

I've tried all kinds of crap -- even tried assigning an arbitrary URI
to the in-memory-datasource instance, then registering this datasource
with the rdf service, which actually causes the browser to crash.

Am I doing something wrong (besides registering my in-memory-
datasource), or is this some kind of ploy to get people to stop using
RDF? Where could I have found relevant documentation (everything I've
read seems to indicate what I'm trying to do is still possible on
Firefox 3.0)?