Skinny

This extension lets you limit the width of any web page, for better readability on big screens.

When a web page has lines of text that run the full width of the page, it can become hard to read on high resolution monitors. If you find yourself making your browser window smaller just so you can read Wikipedia comfortably, this is the extension for you! Just click the Skinny icon to instantly make the page narrower. (The extensions doesn't change any pages until you click the button.) Two vertical bars are added to the page, visible only on hover, that you can drag to change the width. It will keep track of pages that you have set to be 'skinny', except any pages you visit in incognito mode. If there's a site that's not behaving well with this extension let me know and I'll check it out.