User blog comment:Rupert Giles/Layout Changes: Breakpoints and Typography/@comment-26009169-20150519160511/@comment-26009169-20150519170730

The reason for narrowing the article is because you'll have it easier to see the next row and find sentences without moving your eye too much and "getting lost"

Here's the script, save it as a bookmark and click it on the sites you want to be narrow