Examine source code of ProgressBarNT

{
  "manifest_version": 2,
  "name": "ProgressBarNT",
  "description": "A custom new tab page for Firefox.",
  "version": "0.4.0",
  "icons": {
    "48": "imgs/icon_48.png"
  },
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4c92236e-ad5d-40e7-a2b8-69716dcca67c}"
    }
  }
}