root/trunk/modules/version.jsm

const EXPORTED_SYMBOLS = ['ID', 'ITEM', 'VERSION', 'BASE_VERSION', 'NAME', 'compareVersion'];

const ID = 'dta@downthemall.net';
const ITEM = Components.classes["@mozilla.org/extensions/manager;1"]
  .getService(Components.interfaces.nsIExtensionManager)
  .getItemForID(ID);

const VERSION = ITEM.version;
const BASE_VERSION = VERSION.replace(/^([\d\w]+\.[\d\w]+).*?$/, '$1');
const NAME = ITEM.name;

const comparator = 
  Components.classes['@mozilla.org/xpcom/version-comparator;1']
  .getService(Components.interfaces.nsIVersionComparator);

function compareVersion(version, cmp) {
  if (!cmp) {
    [version, cmp] = [VERSION, version];
  }
  return comparator.compare(version, cmp);
}