Examine source code of Guitar Scale Overlay

{
  "manifest_version": 2,
  "name": "Guitar Scale Overlay",
  "version": "1.5.8",
  "description": "Learn guitar scales visually! Interactive neck overlay for YouTube backing tracks. 16 scales, 6/7-string support.",
  "permissions": [
    "storage",
    "*://www.youtube.com/*",
    "*://youtube.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*",
        "*://youtube.com/*"
      ],
      "js": [
        "scales.js",
        "guitar-neck.js",
        "content.js"
      ],
      "css": [
        "styles.css"
      ],
      "run_at": "document_end",
      "all_frames": false
    }
  ],
  "web_accessible_resources": [
    "guitar-neck.svg"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Guitar Scale Overlay",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "applications": {
    "gecko": {
      "id": "guitar-scale-overlay@example.com",
      "strict_min_version": "58.0"
    }
  }
}