Bug 161383 Checkmark indicating active window in Window menu only shows on second menu access

patch by macdoc@interx.net r=neil sr=roc

xpfe/communicator/resources/content/tasksOverlay.xul

@@ -40,7 +40,7 @@
 
       <menu id="windowMenu" label="&windowMenu.label;" accesskey="&windowMenu.accesskey;"
             datasources="rdf:window-mediator" ref="NC:WindowMediatorRoot"
-            onpopupshown="checkFocusedWindow();">
+            onpopupshowing="checkFocusedWindow();">
         <template>
           <rule>
             <menupopup>