Examine source code of wr download

{
  "manifest_version": 2,
  "name": "wr download",
  "description": "Download audio file from wordreference.com definition",
  "version": "0.0.1",
  "icons": {
    "64": "icons/icon38.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "page_action": {
    "default_icon": {
      "19": "icons/icon19.png",
      "38": "icons/icon38.png"
    },
    "default_title": "Download audio file",
    "show_matches": [
      "https://*.wordreference.com/definition/*"
    ],
    "pinned": true,
    "browser_style": true
  },
  "permissions": [
    "activeTab",
    "tabs",
    "downloads"
  ]
}