diff --git a/content/base/public/nsContentUtils.h b/content/base/public/nsContentUtils.h
index 02f67336364..6c38759d810 100644
--- a/content/base/public/nsContentUtils.h
+++ b/content/base/public/nsContentUtils.h
@@ -166,6 +166,9 @@ public:
                                                    const nsAString& aValue);
 
   static void Shutdown();
+  
+  // Checks if two nodes live in document coming from the same origin
+  static nsresult CheckSameOrigin(nsIDOMNode* aNode1, nsIDOMNode* aNode2);
 
 private:
   static nsresult doReparentContentWrapper(nsIContent *aChild,
diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index 5200ab36660..847db2f7e15 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -49,6 +49,10 @@
 #include "nsIDocument.h"
 #include "nsINodeInfo.h"
 #include "nsReadableUtils.h"
+#include "nsIDOMDocument.h"
+#include "nsIURI.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsDOMError.h"
 
 #include "nsIJSContextStack.h"
 #include "nsIDocShell.h"
@@ -350,6 +354,58 @@ nsContentUtils::GetClassInfoInstance(nsDOMClassInfoID aID)
   return sDOMScriptObjectFactory->GetClassInfoInstance(aID);
 }
 
+// static
+nsresult
+nsContentUtils::CheckSameOrigin(nsIDOMNode* aNode1, nsIDOMNode* aNode2)
+{
+  nsCOMPtr<nsIDocument> doc1 = do_QueryInterface(aNode1);
+  if (!doc1) {
+    // Make sure that this is a real node.
+    nsCOMPtr<nsIContent> cont1 = do_QueryInterface(aNode1);
+    if (!cont1) {
+      return NS_ERROR_DOM_SECURITY_ERR;
+    }
+
+    nsCOMPtr<nsIDOMDocument> domDoc1;
+    aNode1->GetOwnerDocument(getter_AddRefs(domDoc1));
+    doc1 = do_QueryInterface(domDoc1);
+    if (!doc1) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+  
+  nsCOMPtr<nsIDocument> doc2 = do_QueryInterface(aNode2);
+  if (!doc2) {
+    // Make sure that this is a real node.
+    nsCOMPtr<nsIContent> cont2 = do_QueryInterface(aNode2);
+    if (!cont2) {
+      return NS_ERROR_DOM_SECURITY_ERR;
+    }
+
+    nsCOMPtr<nsIDOMDocument> domDoc2;
+    aNode2->GetOwnerDocument(getter_AddRefs(domDoc2));
+    doc2 = do_QueryInterface(domDoc2);
+    if (!doc2) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+  
+  if (doc1 == doc2)
+    return NS_OK;
+  
+  nsCOMPtr<nsIURI> uri1;
+  doc1->GetDocumentURL(getter_AddRefs(uri1));
+  nsCOMPtr<nsIURI> uri2;
+  doc2->GetDocumentURL(getter_AddRefs(uri2));
+
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIScriptSecurityManager> securityManager = 
+      do_GetService(NS_SCRIPTSECURITYMANAGER_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+  
+  return securityManager->CheckSameOriginURI(uri1, uri2);
+}
+
 // static
 nsresult
 nsContentUtils::doReparentContentWrapper(nsIContent *aChild,
diff --git a/content/base/src/nsDocument.cpp b/content/base/src/nsDocument.cpp
index 5d695ccfba0..c0812cc987a 100644
--- a/content/base/src/nsDocument.cpp
+++ b/content/base/src/nsDocument.cpp
@@ -2698,6 +2698,12 @@ nsDocument::CreateTreeWalker(nsIDOMNode *aRoot,
                              PRBool aEntityReferenceExpansion,
                              nsIDOMTreeWalker **_retval)
 {
+  *_retval = nsnull;
+  
+  nsresult rv = nsContentUtils::CheckSameOrigin(this, aRoot);
+  if(NS_FAILED(rv))
+    return rv;
+
   return NS_NewTreeWalker(aRoot,
                           aWhatToShow,
                           aFilter,
diff --git a/content/base/src/nsTreeWalker.cpp b/content/base/src/nsTreeWalker.cpp
index 7991a312b7c..b89ccf23d9d 100644
--- a/content/base/src/nsTreeWalker.cpp
+++ b/content/base/src/nsTreeWalker.cpp
@@ -159,6 +159,11 @@ NS_IMETHODIMP nsTreeWalker::GetCurrentNode(nsIDOMNode * *aCurrentNode)
 NS_IMETHODIMP nsTreeWalker::SetCurrentNode(nsIDOMNode * aCurrentNode)
 {
     NS_ENSURE_TRUE(aCurrentNode, NS_ERROR_DOM_NOT_SUPPORTED_ERR);
+
+    nsresult rv = nsContentUtils::CheckSameOrigin(mRoot, aCurrentNode);
+    if(NS_FAILED(rv))
+        return rv;
+
     mCurrentNode = aCurrentNode;
     return NS_OK;
 }
diff --git a/content/xul/document/src/nsXULDocument.cpp b/content/xul/document/src/nsXULDocument.cpp
index 12bc265c9d2..2fc03ef537f 100644
--- a/content/xul/document/src/nsXULDocument.cpp
+++ b/content/xul/document/src/nsXULDocument.cpp
@@ -3214,6 +3214,12 @@ nsXULDocument::CreateTreeWalker(nsIDOMNode *aRoot,
                                 PRBool aEntityReferenceExpansion,
                                 nsIDOMTreeWalker **_retval)
 {
+  *_retval = nsnull;
+
+  nsresult rv = nsContentUtils::CheckSameOrigin(this, aRoot);
+  if(NS_FAILED(rv))
+    return rv;
+
   return NS_NewTreeWalker(aRoot,
                           aWhatToShow,
                           aFilter,