Examine source code of NuTab

{
  "manifest_version": 2,
  "name": "NuTab",
  "short_name": "NuTab",
  "version": "1.1.0",
  "description": "Replaces your start- or new tab page with a minimalistic clock and beautiful backgrounds.",
  "author": "Freddie Lust-Hed",
  "homepage_url": "https://github.com/Musenkishi/nutab",
  "icons": {
    "64": "nutab_logo.svg",
    "192": "nutab_logo.svg",
    "512": "nutab_logo.svg"
  },
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "chrome_settings_overrides": {
    "homepage": "index.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{658a5ee6-3abb-489d-9f48-d7127cc96176}"
    }
  }
}