I would strongly suggest serving this landing page via http/2.0 - your 504 requests over http/1.1 are currently taking 3.5 minutes for me to load 2MB of data.
I misunderstood your original comment. The reason why there were 500 requests is because I was showing a background full of creepyfaces. It made the site look much nicer but it turns out it didn't scale very well.
Turns out the other heads were removed so it's not doing 500 requests anymore. So where does that leave us? Should we keep arguing over the original situation?
There are various guides for enabling it in web servers that support it. It requires HTTPS as a prerequisite.
For testing it in the browser: in Chrome at least, the developer tools Network tab details the protocol of each request/response. I believe Firefox has similar functionality.