They try, but there is not really predictable and simple way to select those fonts in CSS. I've had times when Courier was used on Linux because the MS fonts we installed.
I would prefer they just do font-family: monospace
Is this the problem where it appears almost double spaced? That's what I get on Chrome 58.0.3029.83. And the scrolling performance is horrible, I assume it's some js stuff happening.
https://news.ycombinator.com/item?id=12075623