CSP originally also addressed cross site request forgery (CSRF) attacks, but the anti-CSRF measures have been moved into a separate security specification called the Origin Header proposal.
XSS and CSRF attacks have been used for data theft, Web site defacement, and malware distribution. They're typically made possible by Web application coding errors.
In its specification, Mozilla acknowledges that the ideal solution would be creating Web applications without vulnerabilities. But real world security is a matter of layers so Mozilla feels justified in building a net to catch careless coding.
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