Examine source code of FullWPP

{
  "manifest_version": 2,
  "name": "FullWPP",
  "version": "1.2",
  "description": "Makes whatsapp web fullscreen.",
  "icons": {},
  "content_scripts": [
    {
      "matches": [
        "*://web.whatsapp.com/*"
      ],
      "js": [
        "fullwpp.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{715908f2-d76d-44d3-a3d8-45495adc76c6}"
    }
  }
}