Examine source code of NewTab

{
  "browser_specific_settings": {
    "gecko": {
      "id": "coolnewtab@williamayoub.com",
      "strict_min_version": "57.0"
    }
  },
  "name": "NewTab",
  "version": "1.2.3",
  "description": "A cool new tab",
  "manifest_version": 2,
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "browser_action": {
    "default_popup": "index.html"
  },
  "icons": {
    "16": "logo/logo16.png",
    "48": "logo/logo48.png",
    "128": "logo/logo128.png"
  }
}