Examine source code of Sunshine

{
  "manifest_version": 2,
  "name": "Sunshine",
  "description": "Overlay beautiful shadow effects on any website",
  "version": "0.3.0",
  "icons": {
    "16": "icons/16.png",
    "32": "icons/32.png",
    "48": "icons/48.png",
    "96": "icons/96.png",
    "128": "icons/128.png"
  },
  "permissions": [
    "storage",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d4f7e8a1-9c3b-4f2d-b6a8-1e5f7c9d2b4a}",
      "strict_min_version": "109.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "web_accessible_resources": [
    "shadows/*"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}