diff --git a/widget/public/nsIDMItem.h b/widget/public/nsIDMItem.h
index 7af870dff6d8..bed21dab95b2 100644
--- a/widget/public/nsIDMItem.h
+++ b/widget/public/nsIDMItem.h
@@ -40,10 +40,14 @@ public:
 	// Methods for iterating over children.
 	NS_IMETHOD GetChildCount(PRUint32& count) const = 0;
 	NS_IMETHOD GetNthChild(nsIDMItem*& pItem, PRUint32 item) const = 0;
+	NS_IMETHOD GetSubtreeSize(PRUint32& size) const = 0;
 
 	// Parent access
 	NS_IMETHOD GetParent(nsIDMItem*& pItem) const = 0;
 
+	// Setters
+    NS_IMETHOD SetOpenState(PRBool state) = 0;
+
 	// Methods to query the data model for a specific item displayed within the widget.
 	NS_IMETHOD GetStringPropertyValue(nsString& value, const nsString& itemProperty) const = 0;
 	NS_IMETHOD GetIntPropertyValue(PRInt32& value, const nsString& itemProperty) const = 0;