Off topic (sorry): Can someone explain to me why firefox's "readable view" is randomly not available on some pages, such as this one? I had to manually add "max

Off topic (sorry): Can someone explain to me why firefox's "readable view" is randomly not available on some pages, such as this one? I had to manually add "max-width: 700px" to the html element to read this without straining my eyes. [And funnily enough, author complains about ruining web design when his page is far more readable on a vertical-layout smartphone browser than a 1680x1050 resolution monitor...]