Examine source code of Hack the Form

{
  "name": "Hack the Form",
  "description": "A useful add-on for web developers to view hidden inputs in form.",
  "version": "0.4",
  "manifest_version": 2,
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "background": {
    "scripts": [
      "main.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_icon": "icons/icon-96.png",
    "default_title": "Hack the Form"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "form-hack-reloaded@7s26simon.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}