This should get us going with firefox

calendar/resources/content/calendar.xul

@@ -183,6 +183,7 @@
 <!-- Javascript includes -->
 
 <script type="application/x-javascript" src="chrome://calendar/content/jslib/jslib.js"/>
+<script type="application/x-javascript" src="chrome://communicator/content/utilityOverlay.js"/>
 
 <!-- NEEDED FOR DRAG AND DROP SUPPORT -->
 <script type="application/x-javascript" src="chrome://calendar/content/dragDrop.js"/>

calendar/resources/content/menuOverlay.xul

@@ -40,7 +40,6 @@
 
 <?xml-stylesheet href="chrome://calendar/skin/overlay.css" type="text/css"?> 
 
-<?xul-overlay href="chrome://communicator/content/utilityOverlay.xul"?>
 <?xul-overlay href="chrome://global/content/charsetOverlay.xul"?>
 
 <!DOCTYPE overlay