Examine source code of Realtools

{
  "name": "Realtools",
  "description": "The mini version of Realtools.",
  "version": "2.3.2",
  "manifest_version": 2,
  "permissions": [
    "storage",
    "https://*.horsereality.com/horses/*",
    "https://realtools.shay.cat/*"
  ],
  "browser_action": {
    "default_popup": "popout.html",
    "default_icon": {
      "16": "/images/16.png",
      "32": "/images/32.png",
      "48": "/images/48.png",
      "128": "/images/128.png"
    }
  },
  "icons": {
    "16": "/images/16.png",
    "32": "/images/32.png",
    "48": "/images/48.png",
    "128": "/images/128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.horsereality.com/horses/*"
      ],
      "js": [
        "browser-polyfill.js",
        "constants.js",
        "site-hr/css.js",
        "site-hr/utils.js",
        "site-hr/calculator.js",
        "site-hr/buttons.js",
        "site-hr/layers.js"
      ]
    },
    {
      "matches": [
        "https://realtools.shay.cat/*"
      ],
      "js": [
        "browser-polyfill.js",
        "constants.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{654efe56-3927-4fb3-a1ec-b4e1e551d4ab}"
    }
  }
}