If you are using Google Chrome and have RocketLoader enabled, you may see a console warning like this:
A Parser-blocking, cross-origin script, http://ajax.cloudflare.com/cdn-cgi/nexp/dok3v=e153432b12/cloudflare.min.js, is invoked via document.write
Currently this message in the browser console is just a warning. It is not an error and will not impede your website from functioning in any way.
It is triggered when RocketLoader loads and the warning is specific to mobile devices only. However, RocketLoader is disabled on all mobile devices, so this warning can be safely ignored as it will have no effect on your website and is nothing to be concerned about.