Revisiting the "Cookieless Domain" Recommendation
For a long time one of the recommendations for a faster site has been to “serve your static content from a cookieless domain”. This suggestion shows up in the Google best practices , the Yahoo! performance rules , and in Phil Dixon’s famous Shopzilla case study from Velocity 2009, where he states that implementing this one best practice resulted in a 0.5% improvement in top line revenue. Case closed, right? Well, due to some recent experimentation we have been doing at Etsy , we had reason to believe that people might be taking this too far. Specifically, our testing indicated that serving CSS files from the same domain as the base page might be a performance win. Why is this a Good Idea? CSS blocks page rendering, because if it didn’t then users would get the dreaded flash of unstyled content . This is the reason why another performance recommendation is to put CSS in the head of the document, and to combine CSS files and minify them. Getting CSS to start downloading as