diff --git a/mozilla/extensions/xforms/nsXFormsActionElement.cpp b/mozilla/extensions/xforms/nsXFormsActionElement.cpp
index 6e64d4a0261..9e10594f711 100644
--- a/mozilla/extensions/xforms/nsXFormsActionElement.cpp
+++ b/mozilla/extensions/xforms/nsXFormsActionElement.cpp
@@ -140,8 +140,8 @@ PR_STATIC_CALLBACK(PLDHashOperator) DoDeferredActions(nsISupports * aModel,
                                                       void * data)
 {
   if (aModel && aDeferred) {
-    nsCOMPtr<nsIModelElementPrivate> model =
-      NS_STATIC_CAST(nsIModelElementPrivate*, aModel);
+    nsCOMPtr<nsIModelElementPrivate> model(do_QueryInterface(aModel));
+
     if (aDeferred & DEFERRED_REBUILD)
       model->RequestRebuild();
     if (aDeferred & DEFERRED_RECALCULATE)
@@ -228,13 +228,19 @@ nsXFormsActionElement::SetRecalculate(nsIModelElementPrivate* aModel,
   }
 
   PRUint32 deferred = 0;
-  mDeferredUpdates.Get(aModel, &deferred);
+
+  // It is possible that QI's to an interface that isn't nsISupports (like
+  // nsIModelElementPrivate) could produce different values even from the same
+  // model element.  So we'll convert the model to nsISupports before querying
+  // it or storing it via hashtable.
+  nsCOMPtr<nsISupports> temp(do_QueryInterface(aModel));
+  mDeferredUpdates.Get(temp, &deferred);
   if (aEnable) {
     deferred |= DEFERRED_RECALCULATE;
   } else {
     deferred &= ~DEFERRED_RECALCULATE;
   }
-  mDeferredUpdates.Put(aModel, deferred);
+  mDeferredUpdates.Put(temp, deferred);
   return NS_OK;
 }
 
@@ -247,13 +253,19 @@ nsXFormsActionElement::SetRevalidate(nsIModelElementPrivate* aModel,
   }
 
   PRUint32 deferred = 0;
-  mDeferredUpdates.Get(aModel, &deferred);
+
+  // It is possible that QI's to an interface that isn't nsISupports (like
+  // nsIModelElementPrivate) could produce different values even from the same
+  // model element.  So we'll convert the model to nsISupports before querying
+  // it or storing it via hashtable.
+  nsCOMPtr<nsISupports> temp(do_QueryInterface(aModel));
+  mDeferredUpdates.Get(temp, &deferred);
   if (aEnable) {
     deferred |= DEFERRED_REVALIDATE;
   } else {
     deferred &= ~DEFERRED_REVALIDATE;
   }
-  mDeferredUpdates.Put(aModel, deferred);
+  mDeferredUpdates.Put(temp, deferred);
   return NS_OK;
 }
 
@@ -266,13 +278,19 @@ nsXFormsActionElement::SetRefresh(nsIModelElementPrivate* aModel,
   }
 
   PRUint32 deferred = 0;
-  mDeferredUpdates.Get(aModel, &deferred);
+
+  // It is possible that QI's to an interface that isn't nsISupports (like
+  // nsIModelElementPrivate) could produce different values even from the same
+  // model element.  So we'll convert the model to nsISupports before querying
+  // it or storing it via hashtable.
+  nsCOMPtr<nsISupports> temp(do_QueryInterface(aModel));
+  mDeferredUpdates.Get(temp, &deferred);
   if (aEnable) {
     deferred |= DEFERRED_REFRESH;
   } else {
     deferred &= ~DEFERRED_REFRESH;
   }
-  mDeferredUpdates.Put(aModel, deferred);
+  mDeferredUpdates.Put(temp, deferred);
   return NS_OK;
 }