rem: this.mPrefs.setComplexValue(aName, Components.interfaces.nsISupportsWString, aValue); 
add: var str = Components.classes["@mozilla.org/supports-wstring;1"] .createInstance(Components.interfaces.nsISupportsWString); str.data = aValue; this.mPrefs.setComplexValue(aName, Components.interfaces.nsISupportsWString, str); 
context:   setPref: function(aName, aValue)  {    if (!this.mPrefs) this.init();        var type = this.mPrefs.getPrefType(aName);    try {      if (type == nsIPrefBranch.PREF_STRING) {        this.mPrefs.setComplexValue(aName, Components.interfaces.nsISupportsWString, aValue);      } 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/f0d6d8712b965f68658dd56fab062282d0ac6850/PrefUtils.js/buggy/extensions/inspector/resources/content/jsutil/system/PrefUtils.js