see: http://d.hatena.ne.jp/hasegawayosuke/20130112/p1

eject.jsm

const EXPORTED_SYMBOLS = ["eject"];

Components.utils.import("resource://gre/modules/ctypes.jsm");

const UINT = ctypes.unsigned_int;
const DWORD = ctypes.uint32_t;
const LPCWSTR = ctypes.jschar.ptr;

if (ctypes.size_t.size == 8) {
    var WinABI = ctypes.default_abi;
} else {
    var WinABI = ctypes.winapi_abi;
}
var dll = "winmm.dll";

function eject () {
  var winmm = ctypes.open(dll);
  var mciSendStringW = winmm.declare("mciSendStringW", WinABI, DWORD, LPCWSTR, DWORD, UINT, DWORD);
  return mciSendStringW("set cdaudio door open", 0, 0, 0);
}