Examine source code of AutofillGoogleForms

{
  "manifest_version": 2,
  "name": "AGF",
  "version": "1.0",
  "description": "Autofill Google Forms",
  "icons": {
    "48": "icons/agf.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ba45f2dc-3eef-4b5b-9de8-5221ea538775}"
    }
  },
  "permissions": [
    "storage",
    "https://docs.google.com/forms/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://docs.google.com/forms/*"
      ],
      "js": [
        "main.js"
      ],
      "css": [
        "main.css"
      ]
    }
  ]
}