Examine source code of Phone Caller

{
  "manifest_version": 2,
  "name": "Phone Caller",
  "version": "1.0",
  "description": "Call phone numbers using your default calling app",
  "permissions": [
    "activeTab",
    "contextMenus"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Phone Caller",
    "default_icon": {
      "16": "icons/icon-16.png",
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  },
  "icons": {
    "16": "icons/icon-16.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{904b4c07-476c-47cb-9d48-64eb15b7fa41}"
    }
  }
}