I wouldn't mind resizing the browser window except that with tabbed systems that means you're resizing all of the tabs at the same time.
I tend to think that if you make the width something in the neighborhood of what the NYT, Medium, or other well-known sites use, people won't complain. But I could be wrong!
Cumbersome, but one can change width of a single tab by using the inspector and using the responsive design mode.
Perhaps there is room for another Firefox feature to limit width of a page. Perhaps multi-column mode, where one can for example split the page in 3 columns and each column displays, what could not be fit on the previous column. And resizable columns maybe.
Back when I used an OS that didn't let me scale the UI, I'd occasionally make the browser window narrower to make the lines of text on a site more reasonable, but I definitely appreciated it when sites made it unnecessary for me to do that, by specifying body {max-width: 45em;} or something.
I suspect my site would fall afoul of some of the taste around here but I didn't think Simon's was bad as far as they went.
Dan's is the only one I recall visiting before. And it's memorable because of the maximally wide text width. Personally I would find Dan's site more usable, and visitable, if there was an ordinary text width. Some reasonable default that is more readable.
Just a lil bit of padding here and there could improve the presentation a lot, but I'm guessing the author consider this design kind of a trademark by now.
I much prefer the brutalist look of Drew Devault, Fabien Sanglard, or Dan Luu's site.