Examine source code of QuickMirror

{
  "manifest_version": 2,
  "name": "QuickMirror",
  "version": "1.0",
  "description": "Hover images to show buttons for left-right or up-down mirror using CSS transform.",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "style.css"
      ]
    }
  ],
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "quickmirror@example.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  }
}