Examine source code of Custom New Tab Page

{
  "manifest_version": 2,
  "name": "Custom New Tab Page",
  "version": "1.0.0",
  "description": "Specify a custom URL to be shown when opening a new tab, without changing the address bar content",
  "developer": {
    "name": "MethodGrab",
    "url": "https://github.com/methodgrab/firefox-custom-new-tab-page"
  },
  "icons": {
    "48": "img/icon-48.png",
    "96": "img/icon-96.png"
  },
  "applications": {
    "gecko": {
      "id": "custom-new-tab-page@mint.as",
      "strict_min_version": "57.0"
    }
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  },
  "permissions": [
    "storage"
  ],
  "optional_permissions": [
    "<all_urls>",
    "webRequest",
    "webRequestBlocking"
  ],
  "chrome_url_overrides": {
    "newtab": "app.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}