Examine source code of Spotify to Deezer

{
  "manifest_version": 2,
  "name": "Spotify to Deezer",
  "version": "1.2.0",
  "description": "Open Spotify links in deezer",
  "icons": {
    "48": "icons/spot-x-deezer-48x48.png",
    "400": "icons/spot-x-deezer-400x400.png"
  },
  "permissions": [
    "notifications",
    "contextMenus",
    "https://open.spotify.com/",
    "https://api.deezer.com/"
  ],
  "background": {
    "scripts": [
      "main.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ]
    }
  ]
}