Content Security Policy Officially Part of Firefox
As of March 22, 2011 Content Security Policy is officially released as part of Firefox. Users of Firefox 4 and later now have a working implementation of CSP and can test out the new feature. The easiest way to test it out is to download Firefox and head over to the demo page to see it in action.
Note: you can activate and de-activate the CSP feature by toggling the about:config option