diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 6306b89fc10a..1ae96d223c71 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1550,8 +1550,6 @@ nsDocument::nsDocument(const char* aContentType)
   , mAnimatingImages(true)
   , mViewportType(Unknown)
 {
-  mDefaultElementType = kNameSpaceID_XHTML;
-
   SetContentTypeInternal(nsDependentCString(aContentType));
 
   if (!gDocumentLeakPRLog)
diff --git a/dom/base/test/test_XHRSendData.html b/dom/base/test/test_XHRSendData.html
index 2274643202c3..05e0b4f49c2e 100644
--- a/dom/base/test/test_XHRSendData.html
+++ b/dom/base/test/test_XHRSendData.html
@@ -34,7 +34,7 @@ is(testDoc1.inputEncoding, "windows-1252", "wrong encoding");
 
 testDoc2 = document.implementation.createDocument("", "", null);
 testDoc2.appendChild(testDoc2.createComment(" doc 2 "));
-testDoc2.appendChild(testDoc2.createElementNS(null, "res"));
+testDoc2.appendChild(testDoc2.createElement("res"));
 testDoc2.documentElement.appendChild(testDoc2.createTextNode("text"));
 is(testDoc2.inputEncoding, "UTF-8", "wrong encoding");
 
diff --git a/dom/base/test/unit/test_xml_serializer.js b/dom/base/test/unit/test_xml_serializer.js
index 267fd9c8117a..c74d067a8115 100644
--- a/dom/base/test/unit/test_xml_serializer.js
+++ b/dom/base/test/unit/test_xml_serializer.js
@@ -175,7 +175,7 @@ function test5() {
   // Handling of kids in the null namespace when the default is a
   // different namespace (bug 301260).
   var doc = ParseXML('<root xmlns="ns1"/>')
-  var child = doc.createElementNS(null, 'child');
+  var child = doc.createElement('child');
   doc.documentElement.appendChild(child);
   do_check_serialize(doc);
   do_check_eq(SerializeXML(doc),
diff --git a/dom/html/nsHTMLDocument.cpp b/dom/html/nsHTMLDocument.cpp
index 87cf1379d70c..7bb56d898df9 100644
--- a/dom/html/nsHTMLDocument.cpp
+++ b/dom/html/nsHTMLDocument.cpp
@@ -176,6 +176,7 @@ nsHTMLDocument::nsHTMLDocument()
   // bother initializing members to 0.
 
   mType = eHTML;
+  mDefaultElementType = kNameSpaceID_XHTML;
   mCompatMode = eCompatibility_NavQuirks;
 }
 
diff --git a/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json b/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json
index 272c5e890a5a..8c7b35264d9f 100644
--- a/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json
+++ b/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json
@@ -1,5 +1,7 @@
 {
   "document.characterSet": true,
   "foreignDoc.characterSet": true,
-  "xmlDoc.characterSet": true
+  "xmlDoc.characterSet": true,
+  "xmlElement.namespaceURI": true,
+  "detachedXmlElement.namespaceURI": true
 }
diff --git a/dom/imptests/html/dom/nodes/test_Document-createElement-namespace.html b/dom/imptests/html/dom/nodes/test_Document-createElement-namespace.html
index c9f1a33eaf36..4898eeabc813 100644
--- a/dom/imptests/html/dom/nodes/test_Document-createElement-namespace.html
+++ b/dom/imptests/html/dom/nodes/test_Document-createElement-namespace.html
@@ -24,7 +24,11 @@ function testDoc(doc, contentType) {
                   "Wrong MIME type -- incorrect server config?");
   }
 
-  assert_equals(doc.createElement("x").namespaceURI, "http://www.w3.org/1999/xhtml");
+  var expectedNamespace = contentType == "text/html" ||
+                          contentType == "application/xhtml+xml"
+                          ? "http://www.w3.org/1999/xhtml" : null;
+
+  assert_equals(doc.createElement("x").namespaceURI, expectedNamespace);
 }
 
 // First test various objects we create in JS
diff --git a/testing/web-platform/meta/custom-elements/creating-and-passing-registries/share-registry-create-document.html.ini b/testing/web-platform/meta/custom-elements/creating-and-passing-registries/share-registry-create-document.html.ini
new file mode 100644
index 000000000000..482a2a2df574
--- /dev/null
+++ b/testing/web-platform/meta/custom-elements/creating-and-passing-registries/share-registry-create-document.html.ini
@@ -0,0 +1,5 @@
+[share-registry-create-document.html]
+  type: testharness
+  [Document created by createDocument with HTML namespace should share an existing registry]
+    expected: FAIL
+
diff --git a/testing/web-platform/meta/dom/nodes/Document-constructor.html.ini b/testing/web-platform/meta/dom/nodes/Document-constructor.html.ini
new file mode 100644
index 000000000000..d86bc27bc9a0
--- /dev/null
+++ b/testing/web-platform/meta/dom/nodes/Document-constructor.html.ini
@@ -0,0 +1,5 @@
+[Document-constructor.html]
+  type: testharness
+  [new Document(): URL parsing]
+    expected: FAIL
+
diff --git a/testing/web-platform/meta/dom/nodes/Document-createElement-namespace.html.ini b/testing/web-platform/meta/dom/nodes/Document-createElement-namespace.html.ini
deleted file mode 100644
index 9647b1f7331e..000000000000
--- a/testing/web-platform/meta/dom/nodes/Document-createElement-namespace.html.ini
+++ /dev/null
@@ -1,74 +0,0 @@
-[Document-createElement-namespace.html]
-  type: testharness
-  [Created element's namespace in created XML document]
-    expected: FAIL
-
-  [Created element's namespace in created XHTML document]
-    expected: FAIL
-
-  [Created element's namespace in created SVG document]
-    expected: FAIL
-
-  [Created element's namespace in created MathML document]
-    expected: FAIL
-
-  [Created element's namespace in empty.xml]
-    expected: FAIL
-
-  [Created element's namespace in empty.svg]
-    expected: FAIL
-
-  [Created element's namespace in minimal_html.xml]
-    expected: FAIL
-
-  [Created element's namespace in minimal_html.svg]
-    expected: FAIL
-
-  [Created element's namespace in xhtml.xml]
-    expected: FAIL
-
-  [Created element's namespace in xhtml.svg]
-    expected: FAIL
-
-  [Created element's namespace in svg.xml]
-    expected: FAIL
-
-  [Created element's namespace in svg.svg]
-    expected: FAIL
-
-  [Created element's namespace in mathml.xml]
-    expected: FAIL
-
-  [Created element's namespace in mathml.svg]
-    expected: FAIL
-
-  [Created element's namespace in bare_xhtml.xml]
-    expected: FAIL
-
-  [Created element's namespace in bare_xhtml.svg]
-    expected: FAIL
-
-  [Created element's namespace in bare_svg.xml]
-    expected: FAIL
-
-  [Created element's namespace in bare_svg.svg]
-    expected: FAIL
-
-  [Created element's namespace in bare_mathml.xml]
-    expected: FAIL
-
-  [Created element's namespace in bare_mathml.svg]
-    expected: FAIL
-
-  [Created element's namespace in xhtml_ns_removed.xml]
-    expected: FAIL
-
-  [Created element's namespace in xhtml_ns_removed.svg]
-    expected: FAIL
-
-  [Created element's namespace in xhtml_ns_changed.xml]
-    expected: FAIL
-
-  [Created element's namespace in xhtml_ns_changed.svg]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/dom/nodes/Node-properties.html.ini b/testing/web-platform/meta/dom/nodes/Node-properties.html.ini
new file mode 100644
index 000000000000..2e1731cc21b4
--- /dev/null
+++ b/testing/web-platform/meta/dom/nodes/Node-properties.html.ini
@@ -0,0 +1,8 @@
+[Node-properties.html]
+  type: testharness
+  [xmlElement.namespaceURI]
+    expected: FAIL
+
+  [detachedXmlElement.namespaceURI]
+    expected: FAIL
+