javascript:!function(){var e,t;e='body {margin: auto;margin-left: 100px;max-width: 540px;font-family: "Helvetica Neue", Helvetica, sans-serif;}',t=document.createElement("style"),t.type="text/css",t.appendChild(document.createTextNode(e)),document.getElementsByTagName("head")[0].appendChild(t)}();
You could change the "540" to "900" for your needs. I prefer this to narrowing the window because I prefer the whole screen to have a uniform background color.Edit I don't think it is infaillible, it didn't work on this page, but it works well on pages with no markup. For more complicated site you may try this: https://oxal.org/projects/sakura/bookmark/
What I do myself on sites like this is to use CTRL+ until the text is so large that I can read multiple lines in parallell (that is the secret behind speed reading, but the lines can not be too long of course).
To you. What I or someone not you does is up to them. For example, keeping a window full screen might have a lot of empty/negative space, but sometimes that's the desired effect to cover up all of the other things attempting to grab one's attention without having to hide/minimize other windows.
<meta name="viewport" content="width=device-width, initial-scale=1">
Sites with grey text on grey background I usually skip.
Once Firefox was my web browser because it has a very easy setting for forcing exactly this (black on white).
To be honest I never notice this particular problem because it’s easy to mitigate. The one I do notice is when someone creates an unnecessary minimum width so all the text doesn’t fit. I’m not a huge fan of max width either but it usually is a pretty minor annoyance.