Examine source code of Youtube Grid Customiser

{
  "manifest_version": 2,
  "name": "Youtube Grid Customiser",
  "version": "1.0",
  "description": "Allows customising the number of columns shown on the YouTube homepage.",
  "icons": {
    "48": "icons/border-48.svg"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "ygc.js"
      ]
    }
  ],
  "permissions": [
    "*://*.youtube.com/*",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "max.jp.ward@gmail.com"
    }
  },
  "browser_action": {
    "default_icon": "icons/border-48.svg",
    "default_title": "Youtube Grid Customiser",
    "default_popup": "popup/popup.html"
  }
}