This project is obsolete and not maintained anymore.
XUL's "stringbundle" element has some useful methods, but nsIStringBundle doesn't. This provides a wrapper for nsIStringBundle compatible to "stringbundle".
var bundle = window['piro.sakura.ne.jp']
.stringBundle
.get('chrome://example/locale/example.properties');
bundle.getString('key1');
bundle.getFormattedString('key2', [val1, val2]);