diff --git a/content/base/public/nsIDocument.h b/content/base/public/nsIDocument.h
index ca2aecb060c..58fbc1d0bdb 100644
--- a/content/base/public/nsIDocument.h
+++ b/content/base/public/nsIDocument.h
@@ -91,8 +91,8 @@ class nsIDocumentObserver;
 
 // IID for the nsIDocument interface
 #define NS_IDOCUMENT_IID      \
-{ 0x3b3cb52f, 0xf604, 0x48d5, \
-  { 0xb5, 0x70, 0xf3, 0x25, 0xbb, 0x0a, 0x7a, 0x22 } }
+{ 0x726ce58e, 0x13ab, 0x4c91, \
+  { 0x80, 0x45, 0xa8, 0x7b, 0xfe, 0xd5, 0xfe, 0xcd } }
 
 
 // Flag for AddStyleSheet().
@@ -899,6 +899,13 @@ public:
   virtual void CopyUserData(const nsINode *aObject,
                             nsIDocument *aDestination) = 0;
 
+  /**
+   * Resets and removes a box object from the document's box object cache
+   *
+   * @param aElement canonical nsIContent pointer of the box object's element
+   */
+  virtual void ClearBoxObjectFor(nsIContent *aContent) = 0;
+
 protected:
   ~nsIDocument()
   {
diff --git a/content/base/src/nsDocument.cpp b/content/base/src/nsDocument.cpp
index 506587b0dd1..375a6cfcfb9 100644
--- a/content/base/src/nsDocument.cpp
+++ b/content/base/src/nsDocument.cpp
@@ -106,8 +106,6 @@
 #include "nsPIDOMWindow.h"
 #include "nsIDOMElement.h"
 
-#include "nsIBoxObject.h"
-#include "nsPIBoxObject.h"
 #include "nsXULAtoms.h"
 
 // for radio group stuff
@@ -3228,21 +3226,18 @@ nsDocument::GetBoxObjectFor(nsIDOMElement* aElement, nsIBoxObject** aResult)
   NS_ENSURE_TRUE(content->GetCurrentDoc() == this,
                  NS_ERROR_DOM_WRONG_DOCUMENT_ERR);
   
-  nsresult rv;
-
   *aResult = nsnull;
 
   if (!mBoxObjectTable) {
-    mBoxObjectTable = new nsSupportsHashtable;
+    mBoxObjectTable = new nsInterfaceHashtable<nsISupportsHashKey, nsPIBoxObject>;
+    if (mBoxObjectTable) {
+      mBoxObjectTable->Init(12);
+    }
   } else {
-    nsISupportsKey key(aElement);
-    nsCOMPtr<nsISupports> supports = dont_AddRef(mBoxObjectTable->Get(&key));
-
-    nsCOMPtr<nsIBoxObject> boxObject(do_QueryInterface(supports));
-    if (boxObject) {
-      *aResult = boxObject;
+    // Want to use Get(content, aResult); but it's the wrong type
+    *aResult = mBoxObjectTable->GetWeak(content);
+    if (*aResult) {
       NS_ADDREF(*aResult);
-
       return NS_OK;
     }
   }
@@ -3276,14 +3271,15 @@ nsDocument::GetBoxObjectFor(nsIDOMElement* aElement, nsIBoxObject** aResult)
   }
   contractID += ";1";
 
-  nsCOMPtr<nsIBoxObject> boxObject(do_CreateInstance(contractID.get()));
+  nsCOMPtr<nsPIBoxObject> boxObject(do_CreateInstance(contractID.get()));
   if (!boxObject)
     return NS_ERROR_FAILURE;
 
-  nsCOMPtr<nsPIBoxObject> privateBox(do_QueryInterface(boxObject));
-  privateBox->Init(content);
+  boxObject->Init(content);
 
-  SetBoxObjectFor(aElement, boxObject);
+  if (mBoxObjectTable) {
+    mBoxObjectTable->Put(content, boxObject.get());
+  }
 
   *aResult = boxObject;
   NS_ADDREF(*aResult);
@@ -3291,29 +3287,16 @@ nsDocument::GetBoxObjectFor(nsIDOMElement* aElement, nsIBoxObject** aResult)
   return NS_OK;
 }
 
-NS_IMETHODIMP
-nsDocument::SetBoxObjectFor(nsIDOMElement* aElement, nsIBoxObject* aBoxObject)
+void
+nsDocument::ClearBoxObjectFor(nsIContent* aContent)
 {
-  if (!mBoxObjectTable) {
-    if (!aBoxObject)
-      return NS_OK;
-    mBoxObjectTable = new nsSupportsHashtable(12);
-  }
-
-  nsISupportsKey key(aElement);
-
-  if (aBoxObject) {
-    mBoxObjectTable->Put(&key, aBoxObject);
-  } else {
-    nsCOMPtr<nsISupports> supp;
-    mBoxObjectTable->Remove(&key, getter_AddRefs(supp));
-    nsCOMPtr<nsPIBoxObject> boxObject(do_QueryInterface(supp));
+  if (mBoxObjectTable) {
+    nsPIBoxObject *boxObject = mBoxObjectTable->GetWeak(aContent);
     if (boxObject) {
       boxObject->Clear();
+      mBoxObjectTable->Remove(aContent);
     }
   }
-
-  return NS_OK;
 }
 
 struct DirTable {
diff --git a/content/base/src/nsDocument.h b/content/base/src/nsDocument.h
index 7a946f97d6c..82d894dffb0 100644
--- a/content/base/src/nsDocument.h
+++ b/content/base/src/nsDocument.h
@@ -77,6 +77,9 @@
 #include "nsIDOM3DocumentEvent.h"
 #include "nsCOMArray.h"
 #include "nsHashtable.h"
+#include "nsInterfaceHashtable.h"
+#include "nsIBoxObject.h"
+#include "nsPIBoxObject.h"
 #include "nsIScriptObjectPrincipal.h"
 #include "nsIURI.h"
 #include "nsScriptLoader.h"
@@ -673,6 +676,7 @@ public:
                                        nsIDOMNode *aDest);
   NS_HIDDEN_(void) CopyUserData(const nsINode *aObject,
                                 nsIDocument *aDestination);
+  NS_HIDDEN_(void) ClearBoxObjectFor(nsIContent* aContent);
 
 protected:
 
@@ -784,7 +788,7 @@ protected:
 
   PRUint8 mDefaultElementType;
 
-  nsSupportsHashtable* mBoxObjectTable;
+  nsInterfaceHashtable<nsISupportsHashKey, nsPIBoxObject> *mBoxObjectTable;
 
   // The channel that got passed to StartDocumentLoad(), if any
   nsCOMPtr<nsIChannel> mChannel;
diff --git a/content/base/src/nsGenericElement.cpp b/content/base/src/nsGenericElement.cpp
index 1f46be2a2dc..93e46d72e29 100644
--- a/content/base/src/nsGenericElement.cpp
+++ b/content/base/src/nsGenericElement.cpp
@@ -1850,12 +1850,7 @@ nsGenericElement::UnbindFromTree(PRBool aDeep, PRBool aNullParent)
       document->ForgetLink(this);
     }
 
-    nsCOMPtr<nsIDOMElement> domElement = do_QueryInterface(this);
-
-    if (domElement) {
-      nsCOMPtr<nsIDOMNSDocument> nsDoc = do_QueryInterface(document);
-      nsDoc->SetBoxObjectFor(domElement, nsnull);
-    }
+    document->ClearBoxObjectFor(this);
   }
 
   // Unset things in the reverse order from how we set them in BindToTree
diff --git a/content/xul/content/src/nsXULElement.cpp b/content/xul/content/src/nsXULElement.cpp
index 77d0b3de0ee..a2d57a727a2 100644
--- a/content/xul/content/src/nsXULElement.cpp
+++ b/content/xul/content/src/nsXULElement.cpp
@@ -937,8 +937,7 @@ nsXULElement::UnbindFromTree(PRBool aDeep, PRBool aNullParent)
         // anonymous content that the document is changing.
         document->BindingManager()->ChangeDocumentFor(this, document, nsnull);
 
-        nsCOMPtr<nsIDOMNSDocument> nsDoc(do_QueryInterface(document));
-        nsDoc->SetBoxObjectFor(this, nsnull);
+        document->ClearBoxObjectFor(this);
     }
 
     // mControllers can own objects that are implemented
diff --git a/dom/public/idl/core/nsIDOMNSDocument.idl b/dom/public/idl/core/nsIDOMNSDocument.idl
index 28d6222b31d..b26c5acdef0 100644
--- a/dom/public/idl/core/nsIDOMNSDocument.idl
+++ b/dom/public/idl/core/nsIDOMNSDocument.idl
@@ -43,7 +43,7 @@ interface nsIBoxObject;
 interface nsIDOMLocation;
 
 
-[scriptable, uuid(a6cf90cd-15b3-11d2-932e-00805f8add32)]
+[scriptable, uuid(170763c7-c94e-4db9-98be-e69ac3a02a41)]
 interface nsIDOMNSDocument : nsISupports
 {
   readonly attribute DOMString            characterSet;
@@ -58,6 +58,4 @@ interface nsIDOMNSDocument : nsISupports
   readonly attribute DOMString            referrer;
 
   nsIBoxObject              getBoxObjectFor(in nsIDOMElement elt);
-  void                      setBoxObjectFor(in nsIDOMElement elt,
-                                            in nsIBoxObject boxObject);
 };