Examine source code of Image Size Comparator

{
  "manifest_version": 2,
  "name": "Image Size Comparator",
  "version": "1.0",
  "description": "Compare displayed and actual image sizes. Warns if aspect ratio is distorted.",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "style.css"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Image Size Comparator"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d6362148-0b2e-4c93-8951-a05668425314}"
    }
  }
}