[zelphirkalt]

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.