Just updated to FF 58 and it no longer renders any HTML in the viewport - the viewport is completely blank. I've rebooted the machine, and tried turning off tracking protection; neither of which had any effect. The page title is correctly displayed on the tab. If I view source, I see what looks like a complete HTML document. If I open developer tools, there's only one element in the DOM (html). This occurs on every website I visit. Comparing the attributes of the html tag in the source and developer tools, it looks like JS is running and styles seem to be applied to that single html element. See the attached for to see what I'm seeing.