var reg = new Array(0x80000000, 0x80000005, 0x80000001, 0x80000002, 0x80000003);
// reg values:
// 0: HKEY_CLASSES_ROOT = 0x80000000
// 1: HKEY_CURRENT_CONFIG = 0x80000005
// 2: HKEY_CURRENT_USER = 0x80000001
// 3: HKEY_LOCAL_MACHINE = 0x80000002
// 4: HKEY_USERS = 0x80000003
var regkey = Components.classes["@mozilla.org/windows-registry-key;1"].createInstance(Components.interfaces.nsIWindowsRegKey);
regkey.open(reg[2], 'Software\\Microsoft\\Notepad', Components.interfaces.nsIWindowsRegKey.ACCESS_READ);

alert(regkey.readStringValue("lfFaceName"));