Examine source code of Image Resizer

{
  "manifest_version": 2,
  "name": "image-resizer",
  "version": "1.8.0",
  "developer": {
    "name": "Eliot van Uytfanghe (https://eliotvu.com) <contact@eliotvu.com>",
    "url": "https://eliotvu.com"
  },
  "description": "Resize/Scale any image on the web by dragging at an image!",
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  },
  "icons": {
    "48": "icon-x64.png"
  },
  "applications": {
    "gecko": {
      "id": "jid0-hd39BGK3EuIbK47rGW3fZdR163o@jetpack",
      "strict_min_version": "42.0"
    }
  },
  "permissions": [
    "storage"
  ],
  "background": {
    "scripts": [
      "lib/main.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "data/imageResizer.js"
      ],
      "css": [
        "data/imageResizer.css"
      ],
      "run_at": "document_start"
    }
  ]
}