Examine source code of new tab custom url

{
  "manifest_version": 2,
  "name": "new tab custom url",
  "version": "1.1",
  "description": "choose a url to open on new tab",
  "permissions": [
    "storage",
    "tabs",
    "scripting"
  ],
  "browser_action": {
    "default_popup": "options.html"
  },
  "options_page": "options.html",
  "chrome_url_overrides": {
    "newtab": "newtab.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8f7e4483-51f5-48db-b156-c61fb28dcf85}"
    }
  }
}