UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36

Steps to reproduce the problem:
1. Go to:  https://gauntface.com/blog/2016/09/16/testing-for-the-web
2. Open DevTools and capture a filmstrip of the page loading
3. Hard refresh the page, ctrl + shift + r, on a slow connection (I noticed this when testing on a bus with sketchy wifi) 

What is the expected behavior?
I'd expect the fallback font to be used almost immediately for h1 - h6 elements due to font-display: optional being used in the page.

What went wrong?
After 1.53s of the page loading there is still no font displayed for the title.

This could be any range of issues:

1.) 'Optional' has a long timeout period, the spec only has a "recommendation" of "Gives the font face an extremely small block period (100ms or less is recommended in most cases) and a 0s swap period."
2.) I've meesed up the `font-display: optional` CSS, you can see it inlined at the top of the page
3.) I'm mis-understanding how it should work
4.) font-display is implemented but not with this option

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 59.0.3071.115  Channel: n/a
OS Version: 
Flash Version: 

It's hard to debug any of the above as I'm not sure if / how devtools can be used to examine CSS values that aren't associated with a DOM element.