Examine source code of EasyWPP

{
  "manifest_version": 2,
  "name": "EasyWPP",
  "version": "1.1.0",
  "description": "Envie mensagens no WhatsApp Web sem precisar salvar o contato! Selecione, clique com o botão direito e inicie a conversa.",
  "permissions": [
    "contextMenus",
    "tabs"
  ],
  "icons": {
    "16": "images/icon-16.png",
    "48": "images/icon-48.png",
    "128": "images/icon-128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{9de1e88f-81ef-459d-995b-8da61cf1335a}"
    }
  }
}