Examine source code of Check iframe

{
  "manifest_version": 2,
  "name": "Check iframe",
  "version": "1.8.0",
  "description": "Firefox add-on that indicates if the current web page uses iframes or frames and allows you to browse through them.",
  "homepage_url": "https://github.com/CarlosAMolina/checkIframe",
  "icons": {
    "123": "icons/addonIcon.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/i_gray.png",
    "default_title": "CheckIframe",
    "default_popup": "popup/popup.html"
  },
  "content_scripts": [
    {
      "all_frames": false,
      "run_at": "document_end",
      "matches": [
        "https://*/*",
        "http://*/*",
        "file:///*"
      ],
      "js": [
        "content_scripts/check-and-border.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background_scripts/background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      },
      "id": "{117d8485-1088-4ce1-9050-5e9a05e6a8ee}"
    },
    "gecko_android": {}
  }
}