Examine source code of Check

{
  "manifest_version": 2,
  "name": "Check",
  "description": "Verify breaking news online",
  "version": "2.5.13",
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Ctrl+Shift+L"
      },
      "description": "Verify breaking news online"
    }
  },
  "background": {
    "persistent": true,
    "page": "background.html"
  },
  "browser_action": {
    "default_icon": "check19-in.png",
    "default_title": "Check"
  },
  "content_scripts": [
    {
      "run_at": "document_end",
      "matches": [
        "https://*/*",
        "http://*/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "icons": {
    "48": "check48.png",
    "128": "check128.png"
  },
  "permissions": [
    "activeTab",
    "contextMenus"
  ],
  "web_accessible_resources": [
    "popup.html"
  ],
  "externally_connectable": {
    "matches": [
      "https://checkmedia.org/"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{2070efa6-8cd3-4318-b3d3-ff4c87ea564c}"
    }
  }
}