See tests at <http://w3c-test.org/webapps/DOMCore/tests/submissions/Ms2ger/Node-insertBefore.html> and <http://w3c-test.org/webapps/DOMCore/tests/submissions/Ms2ger/Node-replaceChild.html>.
Tests are now at <http://w3c-test.org/dom/nodes/Node-insertBefore.html> and <http://w3c-test.org/dom/nodes/Node-replaceChild.html>, and appear to pass.