Examine source code of Vialer Click-to-Dial

{
  "manifest_version": 2,
  "name": "Vialer Klik-en-bel",
  "description": "Eenvoudig bellen met één klik in je browser. De extensie die telefoonnummers direct herkent én belt.",
  "version": "3.2.5",
  "icons": {
    "16": "/brand/logo-16.png",
    "24": "/brand/logo-24.png",
    "48": "/brand/logo-48.png",
    "96": "/brand/logo-96.png",
    "128": "/brand/logo-128.png",
    "192": "/brand/logo-192.png",
    "512": "/brand/logo-512.png"
  },
  "default_locale": "en",
  "permissions": [
    "storage",
    "contextMenus",
    "notifications",
    "https://api.segment.io/*",
    "https://partner.voipgrid.nl/api/*",
    "https://freedom.voys.nl/api/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Click-to-dial",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_end",
      "js": [
        "content-scripts/content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "voipgrid@jetpack"
    }
  }
}