Examine source code of Customizable web home

{
  "manifest_version": 2,
  "name": "__MSG_extensionName__",
  "description": "__MSG_extensionDescription__",
  "default_locale": "en",
  "browser_specific_settings": {
    "gecko": {
      "id": "customizable-web-home@by.juanorith"
    }
  },
  "version": "0.1",
  "icons": {
    "32": "images/icon.svg"
  },
  "permissions": [
    "storage",
    "unlimitedStorage"
  ],
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "chrome_settings_overrides": {
    "homepage": "index.html"
  }
}