rem: var str = Components.classes["@mozilla.org/supports-wstring;1"] .createInstance(Components.interfaces.nsISupportsWString); 
add: var str = Components.classes["@mozilla.org/supports-string;1"] .createInstance(Components.interfaces.nsISupportsString); 
context:   setPref: function(aName, aValue)  {    if (!this.mPrefs) this.init();        var type = this.mPrefs.getPrefType(aName);    try {      if (type == nsIPrefBranch.PREF_STRING) {        var str = Components.classes["@mozilla.org/supports-wstring;1"]                            .createInstance(Components.interfaces.nsISupportsWString);        str.data = aValue;        this.mPrefs.setComplexValue(aName, Components.interfaces.nsISupportsWString, str);      } else if (type == nsIPrefBranch.PREF_BOOL) {        this.mPrefs.setBoolPref(aName, aValue);      } else if (type == nsIPrefBranch.PREF_INT) {        this.mPrefs.setIntPref(aName, aValue);      }    } catch(ex) {      debug("ERROR: Unable to write pref \"" + aName + "\".\n");    }  },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/3703f3c61bce0c45d03ff380dc6b806f944ecb73/PrefUtils.js/clean/extensions/inspector/resources/content/jsutil/system/PrefUtils.js