Examine source code of Outline Headings

{
  "manifest_version": 2,
  "name": "Outline Headings",
  "version": "1.0",
  "description": "A Firefox extension to outline headings on websites.",
  "permissions": [
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "random_gecko_id@gmail.com"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "contentScript.js"
      ]
    }
  ]
}