This Greasemonkey script adds options to StackOverflow to

1. expand answer box
2. expand code box
3. resize code font size
4. widen the entire page
5. remove sidebar

Source: https://github.com/yodog/userscripts/blob/master/stackoverflow_code_box_options.user.js

Tested on Firefox 52 ESR
Still wondering if I'll be upgrading to webextensions
Probably not

Feedback much appreciated