Examine source code of reddit-extras

{
  "manifest_version": 2,
  "name": "reddit-extras",
  "description": "Adds some tools to reddit",
  "version": "1.2.0",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://old.reddit.com/*"
      ],
      "css": [
        "src/style.css"
      ],
      "js": [
        "src/hacks.js"
      ],
      "run_at": "document_idle"
    }
  ]
}