Examine source code of Duo Strength

{
  "name": "Duo Strength",
  "description": "Adds individual skill strengths back into the duolingo webpage, similar to data on duome.eu",
  "version": "2.1.0",
  "manifest_version": 2,
  "icons": {
    "16": "icons/icon_16.png",
    "32": "icons/icon_32.png",
    "48": "icons/icon_48.png",
    "64": "icons/icon_64.png",
    "128": "icons/icon_128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "page_action": {
    "show_matches": [
      "https://www.duolingo.com/*",
      "https://preview.duolingo.com/*",
      "https://www-internal.duolingo.com/*"
    ],
    "default_icon": {
      "16": "icons/icon_16.png",
      "32": "icons/icon_32.png",
      "48": "icons/icon_48.png",
      "64": "icons/icon_64.png",
      "128": "icons/icon_128.png"
    },
    "default_title": "Duo Strength",
    "default_popup": "options.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.duolingo.com/*",
        "https://preview.duolingo.com/*",
        "https://www-internal.duolingo.com/*"
      ],
      "js": [
        "duoStrength.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "images/focus.svg",
    "images/defocus.svg",
    "images/popout.svg",
    "images/loading.svg",
    "styles/stylesheet.css",
    "defaultOptions.json",
    "disabledOptions.json"
  ],
  "permissions": [
    "storage"
  ],
  "options_ui": {
    "page": "options.html",
    "open_in_tab": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{911cd95f-2518-40ca-b122-a3d26b0d727b}"
    }
  }
}