diff --git a/toolkit/content/widgets/editor.xml b/toolkit/content/widgets/editor.xml
index 69353b9fc2a0..31ea33657b3c 100644
--- a/toolkit/content/widgets/editor.xml
+++ b/toolkit/content/widgets/editor.xml
@@ -115,6 +115,9 @@
       <property name="webBrowserFind"
                 readonly="true"
                 onget="return this.docShell.QueryInterface(Components.interfaces.nsIInterfaceRequestor).getInterface(Components.interfaces.nsIWebBrowserFind);"/>
+      <property name="markupDocumentViewer"
+                readonly="true"
+                onget="return this.docShell.contentViewer.QueryInterface(Components.interfaces.nsIMarkupDocumentViewer);"/>
       <property name="editingSession"
                 readonly="true"
                 onget="return this.webNavigation.QueryInterface(Components.interfaces.nsIInterfaceRequestor).getInterface(Components.interfaces.nsIEditingSession);"/>