PageSpeed: Serve static content from a cookieless domain (deprecated)
Serving static resources from a cookieless domain reduces the total size of requests made for a page.
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Details from Google
Static content, such as images, JS and CSS files, don't need to be accompanied by cookies, as there is no user interaction with these resources. You can decrease request latency by serving static resources from a domain that doesn't serve cookies. This technique is especially useful for pages referencing large volumes of rarely cached static content, such as frequently changing image thumbnails, or infrequently accessed image archives. We recommend this technique for any page that serves more than 5 static resources. (For pages that serve fewer resources than this, it's not worth the cost of setting up an extra domain.)
To reserve a cookieless domain for serving static content, register a new domain name and configure your DNS database with a CNAME record that points the new domain to your existing domain A record. Configure your web server to serve static resources from the new domain, and do not allow any cookies to be set anywhere on this domain. In your web pages, reference the domain name in the URLs for the static resources.
If you host your static files using a CDN, your CDN may support serving these resources from another domain. Contact your CDN to find out.