Oh, that's a great idea. I see Firefox also has this in the settings under Accessibility. I guess I never looked there because I don't think of myself as disabled. (Maybe I should.)
More and more - especially on Apple products - Accessibility is the "customization" menu, not the "disabled support" it used to be.
Size increases, animation decreases (when your iPhone is getting old, turn off animation and behold it operating super fast!), etc can all be found there.
I zoom websites until they "feel right" which is usually something close to "they are as wide as the window I have them in" - HN is a few taps up from "actual size".