CSP, as described in the above URL, is a proposal to enhance site security by allowing web authors to restrict what sorts of capabilities a page has.
Implementing this would be a boon for web authors trying to reduce XSS and similar attacks.
I talked to Sid via chat. He said he'd thrilled if we implemented CSP. It might be the right time to review the spec in detail and start a prototype implementation.
*** This bug has been marked as a duplicate of bug 53572 ***