Examine source code of SureVoIP

{
  "manifest_version": 2,
  "name": "SureVoIP",
  "description": "SureVoIP Call and SMS Browser Add-on",
  "version": "4.0.3",
  "author": "SureVoIP",
  "browser_action": {
    "default_icon": {
      "16": "images/icon-16.png",
      "32": "images/icon-32.png"
    },
    "default_title": "SureVoIP"
  },
  "permissions": [
    "https://api.surevoip.co.uk/calls",
    "https://api.surevoip.co.uk/sms",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "css": [
        "css/CustomCss.css"
      ],
      "js": [
        "js/jquery-3.5.1.min.js",
        "js/SureVoIP.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "images/*"
  ],
  "icons": {
    "16": "images/icon-16.png",
    "32": "images/icon-32.png",
    "48": "images/icon-48.png",
    "128": "images/icon-128.png"
  },
  "background": {
    "scripts": [
      "js/jquery-3.5.1.min.js",
      "js/background.js"
    ]
  }
}