Examine source code of Image Focus Dimmer

{
  "manifest_version": 2,
  "name": "Image Focus Dimmer",
  "version": "1.0",
  "description": "Dim the whole page except the image under the cursor.",
  "permissions": [],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "style.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{82e191d7-4e10-426f-bb56-656381e6d0ac}"
    }
  }
}