Firefox is leaking URLs data across domain, by not restricting javascript’s “location” method.  How does it work?

A “proof of concept” exploit for the vulnerability exists (for more, check this out).

1. A user browses to the attacker site.
2. That attacker opens a new window in Twitter from attacker site.
3. If the victim is signed in to twitter, then the user gets redirected to a URL that contains a personal twitter ID.
4. The attacker can now query the new window on the URL and obtain the victim’s personal twitter ID.

On previous versions of Firefox, this attack would fail:

There was a regression in Firefox 16 that allowed this attack to work: