Examine source code of Dictionary Panel

{
  "manifest_version": 2,
  "name": "Dictionary Panel",
  "version": "1.0.0",
  "description": "A extension that display the dictionary queried result of selection text in a panel.",
  "permissions": [
    "menus"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "page_action": {},
  "browser_specific_settings": {
    "gecko": {
      "id": "jid1-efsrvlFOR8ZWKw@jetpack",
      "strict_min_version": "57.0"
    }
  }
}