I think that is not so simple to solve. Limit it to some column width? Someone will complain that it only uses one third of their screen. Unlimited width? Someone will complain about whole width text. But the good thing is, that there is reader mode and evem if there wasn't, you could zoom in or resize the browser window or send to new window and resoze only that.
Yeah, most browsers do have reader mode now. I honestly don't love them because they're typically not customizable, and are sometimes too narrow for my taste.
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!
Firefox reader mode is a little bit customizable. Font size column width and so.
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.
