diff --git a/mozilla/content/base/src/nsDocument.cpp b/mozilla/content/base/src/nsDocument.cpp
index 7c972c5bde3..f087808937d 100644
--- a/mozilla/content/base/src/nsDocument.cpp
+++ b/mozilla/content/base/src/nsDocument.cpp
@@ -4414,14 +4414,36 @@ nsresult
 nsDocument::CreateElem(nsIAtom *aName, nsIAtom *aPrefix, PRInt32 aNamespaceID,
                        PRBool aDocumentDefaultType, nsIContent **aResult)
 {
+  nsresult rv;
+#ifdef DEBUG
+  nsIParserService *parserService = nsContentUtils::GetParserServiceWeakRef();
+  NS_ASSERTION(parserService, "Can't get parserService to check name.");
+  if (parserService) {
+    nsAutoString qName;
+    if (aPrefix) {
+      aPrefix->ToString(qName);
+      qName.Append(':');
+    }
+    const char *name;
+    aName->GetUTF8String(&name);
+    AppendUTF8toUTF16(name, qName);
+
+    const PRUnichar *colon;
+    rv = parserService->CheckQName(qName, PR_TRUE, &colon);
+    NS_ASSERTION(NS_SUCCEEDED(rv),
+                 "Don't pass invalid names to nsDocument::CreateElem, "
+                 "check caller.");
+  }
+#endif
+
   *aResult = nsnull;
   
   PRInt32 elementType = aDocumentDefaultType ? mDefaultElementType :
                                                aNamespaceID;
 
   nsCOMPtr<nsINodeInfo> nodeInfo;
-  nsresult rv = mNodeInfoManager->GetNodeInfo(aName, aPrefix, aNamespaceID,
-                                              getter_AddRefs(nodeInfo));
+  rv = mNodeInfoManager->GetNodeInfo(aName, aPrefix, aNamespaceID,
+                                     getter_AddRefs(nodeInfo));
   NS_ENSURE_SUCCESS(rv, rv);
 
   return CreateElement(nodeInfo, elementType, aResult);
diff --git a/mozilla/content/base/src/nsNodeInfoManager.cpp b/mozilla/content/base/src/nsNodeInfoManager.cpp
index 05268bf1f2e..741c6330632 100644
--- a/mozilla/content/base/src/nsNodeInfoManager.cpp
+++ b/mozilla/content/base/src/nsNodeInfoManager.cpp
@@ -172,6 +172,8 @@ nsNodeInfoManager::GetNodeInfo(nsIAtom *aName, nsIAtom *aPrefix,
                                PRInt32 aNamespaceID, nsINodeInfo** aNodeInfo)
 {
   NS_ENSURE_ARG_POINTER(aName);
+  NS_ASSERTION(!aName->Equals(EmptyString()),
+               "Don't pass an empty string to GetNodeInfo, fix caller.");
 
   nsINodeInfo::nsNodeInfoInner tmpKey(aName, aPrefix, aNamespaceID);
 
diff --git a/mozilla/content/html/document/src/nsHTMLDocument.cpp b/mozilla/content/html/document/src/nsHTMLDocument.cpp
index 32889736101..48b7a9f64a3 100644
--- a/mozilla/content/html/document/src/nsHTMLDocument.cpp
+++ b/mozilla/content/html/document/src/nsHTMLDocument.cpp
@@ -4141,6 +4141,15 @@ nsHTMLDocument::CreateElem(nsIAtom *aName, nsIAtom *aPrefix,
                "HTML elements in an HTML document should have "
                "kNamespaceID_None as their namespace ID.");
 
+  if (IsXHTML() &&
+      (aDocumentDefaultType || aNamespaceID == kNameSpaceID_XHTML)) {
+    nsCAutoString name, lcName;
+    aName->ToUTF8String(name);
+    ToLowerCase(name, lcName);
+    NS_ASSERTION(lcName.Equals(name),
+                 "aName should be lowercase, fix caller.");
+  }
+
   return nsDocument::CreateElem(aName, aPrefix, aNamespaceID,
                                 aDocumentDefaultType, aResult);
 }
diff --git a/mozilla/editor/libeditor/base/nsEditor.cpp b/mozilla/editor/libeditor/base/nsEditor.cpp
index 22d3bc6a548..69d508fdf65 100644
--- a/mozilla/editor/libeditor/base/nsEditor.cpp
+++ b/mozilla/editor/libeditor/base/nsEditor.cpp
@@ -5066,6 +5066,14 @@ nsEditor::CreateHTMLContent(const nsAString& aTag, nsIContent** aContent)
   if (!doc)
     return NS_ERROR_FAILURE;
 
+  // XXX Wallpaper over editor bug (editor tries to create elements with an
+  //     empty nodename).
+  if (aTag.IsEmpty()) {
+    NS_ERROR("Don't pass an empty tag to nsEditor::CreateHTMLContent, "
+             "check caller.");
+    return NS_ERROR_FAILURE;
+  }
+
   nsCOMPtr<nsIAtom> tag = do_GetAtom(aTag);
   if (!tag)
     return NS_ERROR_OUT_OF_MEMORY;