I use a widescreen display on which many websites render dense text that occupies the full width. This makes it hard to read long form content. One solution is to resize the browser window. Another easier solution I have found is to use Viewport Resizer.
This is a bookmarklet that is aimed at web developers who want to test how their websites resized to smartphone, tablet and notebook display sizes. However, I have found that this is a good way to reduce the width of text on a website in a natural way.
Viewport Resizer can be installed easily by dragging the bookmarklet to the bookmarks bar in Chrome. Click on the bookmark when viewing any website and it offers display sizes of different types of devices. I like to pick the tablet size. The website is rendered in a nice format for reading 🙂
Tried with: Chrome 42.0.2311.135 (x64) and Ubuntu 14.04