Fix for bug 52966, blank first item in session history popup associated with URLBar. r=hewitt, sr=radha.

suite/browser/navigator.xul

@@ -296,7 +296,7 @@ Contributor(s): ______________________________________. -->
           <menubutton class="menubutton-icon" id="ubhist">
             <menupopup id="ubhist-popup" popupalign="topright" popupanchor="bottomright"
                        oncreate="createUBHistoryMenu(event.target);" oncommand="executeUrlBarHistoryCommand(event.target);"> 
-              <menuitem value=" "/>
+              <menuitem value="&nothingAvailable.label;" index="nothing_available"/>
             </menupopup>                       
           </menubutton>
           

suite/locales/en-US/chrome/browser/navigator.dtd

@@ -11,6 +11,8 @@
 <!ENTITY mainWindow.titlemodifiermenuseparator " - ">
 <!ENTITY viewsourcetitle.preface "Source for: ">
 
+<!ENTITY nothingAvailable.label "(Nothing Available)">
+
 <!ENTITY browserCmd.label					"New Navigator Window">
 <!ENTITY browserCmd.accesskey				"n">
 <!ENTITY openCmd.label "Open Web Location...">