Examine source code of Grayscale Toggle

{
  "manifest_version": 2,
  "name": "Grayscale Toggle",
  "version": "1.0",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "description": "Toggle grayscale for websites.",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{13451d7b-7ea0-4586-a244-37aa31224dbc}"
    }
  }
}