NoCoffee is an extension by Aaron Leventhal that simulates different visual impairments and demonstrates how web content would be seen through each of these impairments. You can read more about it in Aaron's post.
This version offers modest updates and a WebExtension port so it will work on Firefox as well.
Install dependencies by running npm install.
You can lint with npm test.
To test it in a browser, you can do npm start:firefox or npm start:chrome.
npm run build will give you a zip file.