[Minor] Add missed prefwindow id

Author: moisseev

chrome/received/content/options.xul

@@ -3,7 +3,7 @@
 <?xml-stylesheet href="chrome://global/skin/global.css" type="text/css"?>
 <?xml-stylesheet type="text/css" href="chrome://messenger/skin/preferences/preferences.css"?>
 
-<prefwindow title="Received options" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+<prefwindow id="receivedOptions" title="Received options" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
     <prefpane>
         <preferences>
             <preference id="pref_regexp" name="extensions.received.regexp" title="Regular expression with capturing parentheses" type="string" />