Examine source code of Duolingo Progress Bar

{
  "manifest_version": 2,
  "name": "Duolingo Progress Bar",
  "description": "A linear progress bar for your Duolingo courses",
  "version": "0.6",
  "content_scripts": [
    {
      "matches": [
        "https://www.duolingo.com/*",
        "http://www.duolingo.com/*"
      ],
      "js": [
        "intercept.js",
        "content.js"
      ],
      "css": [
        "scrollbar.css",
        "style.css"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_action": {
    "default_icon": {
      "16": "icon/16.png",
      "32": "icon/32.png",
      "48": "icon/48.png",
      "128": "icon/128.png"
    }
  },
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "128": "icon/128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{e0ce7f78-fbb0-4123-b19c-c62ea2eca13d}"
    }
  }
}