Examine source code of Inbox Zero Cats for Gmail

{
  "manifest_version": 2,
  "name": "Inbox Zero Cats for Gmail",
  "version": "3.0.0",
  "description": "Adds a random cat to the empty state of Gmail inbox",
  "icons": {
    "16": "images/icon_16.png",
    "48": "images/icon_48.png",
    "128": "images/icon_128.png",
    "256": "images/icon_256.png",
    "512": "images/icon_512.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/*"
      ],
      "js": [
        "index.js"
      ],
      "css": [
        "styles.css"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "storage",
    "unlimitedStorage"
  ],
  "options_ui": {
    "page": "options/index.html",
    "open_in_tab": true
  },
  "browser_action": {
    "default_icon": {
      "16": "images/icon_16.png",
      "48": "images/icon_48.png",
      "128": "images/icon_128.png"
    },
    "default_title": "Inbox Zero Cats for Gmail",
    "default_popup": "popup/index.html",
    "browser_style": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{1d541bdc-d07e-46ec-a911-aebd8f0f004e}"
    }
  }
}