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. Ge...