XSS due to window.dialogArguments being readable cross-domain — Mozilla

Security researcher Hidetake Jo of Microsoft Vulnerability Research reported that the properties set on an object passed to showModalDialog were readable by the document contained in the dialog, even when the document was from a different domain. This is a violation of the same-origin policy and could result in a website running untrusted JavaScript if it assumed the dialogArguments could not be initialized by another site.