Examine source code of WhatsappSender

{
  "name": "WhatsappSender",
  "description": "Send web api message to a specified number",
  "version": "0.0.2",
  "manifest_version": 2,
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{01bc8e18-5abb-4681-bcbb-ba6834ae0080}"
    }
  }
}