Examine source code of Search Result Enumerator

{
  "manifest_version": 2,
  "name": "Search Result Enumerator",
  "version": "1.1",
  "description": "Adds numbers to Google search results, allowing you to navigate them by pressing the corresponding key.",
  "icons": {
    "128": "icons/icon_1.png"
  },
  "permissions": [
    "activeTab",
    "https://www.google.com/"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.google.com/search*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{8fe2c178-a7e9-4819-867f-258b8ced836c}"
    }
  }
}