Mozilla's RDF API has been architectured to follow the specs RDF Model and Syntax 1999 and RDF Schema 1999. These specs are replaced with RDF Primer 2004 and its five siblings. All of these are linked on RDF W3C RDF.
On top of that, bug 122846 aims at exposing RDF to web content, which requires a thorough security review as well as a strict specifications of the APIs. Which are not given on the current APIs in Mozilla.