Just an information: Peter Szinek, a friend of mine is about to release the Mozilla DOM W3C Connector he implemented. It allows you to access the Mozilla DOM as W3C DOM from within Java when embedding Mozilla. This is fundamental if you want to use standard XML tools and libraries to operate directly on Mozilla DOM, e.g. XML, XSLT, XPath, XQuery. Read more in his original post.
We’ve been using it for few months and it proved to be stable. The bad guy seems to be sometimes JavaXPCOM ;)