Mostly abandoned in favour of a greasemonkey script since this only needs JS/HTML/CSS to implement. Latest updates are available from here:

https://greasyfork.org/en/scripts/39077-pixel-art-zoom

Install

• License: MIT License
• Weekly downloads: 0
• Average daily users: 24
• Rating: 4/5 of 2 ratings
• Created: 2018-01-27 23:25:54
• Last updated: 2018-06-26 23:50:08
• Homepage:
• Support site and email
• Orig: https://addons.mozilla.org/en-US/firefox/addon/pixel-art-zoom1/
• API: {e7feae1e-5b35-4867-9248-345a974dc65a}