This might be on your radar already, but the rendering is broken in Firefox. I'm using version 60.8.0esr, which is what I get with "apt-get install firefox".

When I open the link I see the table of contents on the left and a bunch of empty white space. Scrolling down, the content eventually comes into view, but scrolls on top of the table of contents, making it impossible to click.

I'm blocking the google fonts site, so maybe that's part of the problem.