rem: window.open(parent.hPrefWindow.getPref("localizedstring", "editor.spellcheckers.url")); 
add: var formatter = Components.classes["@mozilla.org/toolkit/URLFormatterService;1"] .getService(Components.interfaces.nsIURLFormatter); window.open(formatter.formatURLPref("spellchecker.dictionaries.download.url")); 
context: function SelectLanguage(aTarget) {  try {    if (aTarget.value != "more-cmd")      gLastSelectedLang = aTarget;    else {      window.open(parent.hPrefWindow.getPref("localizedstring",                                             "editor.spellcheckers.url"));      if (gLastSelectedLang)        document.getElementById("languageMenuList").selectedItem = gLastSelectedLang;    }  } catch (ex) {    dump(ex);  }}
meta: 5459	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/5459/32c7a0d4e612dcd294fe8d0fa884355c6e7f2c61/pref-composing_messages.js/buggy/mailnews/compose/prefs/resources/content/pref-composing_messages.js