You’re confusing the JavaScript keyword Infinity, which has been around forever, with the CSS keyword infinity, which has only been around for 2–3 years <https://caniuse.com/mdn-css_types_calc-keyword_infinity>.

And actually I’d be quite surprised if the infinity keyword is even relevant here; I would expect the same results if you changed each calc(infinity * 1px) to 9999999999999999px. Firefox (and, if you go far enough back, IE) will still ignore overly large height declarations, and WebKit-heritage browsers will clamp it.