Examine source code of Slowed & Reverb

{
  "manifest_version": 3,
  "name": "Slowed & Reverb",
  "version": "1.0.0",
  "description": "Real-time speed, reverb, EQ, and stereo effects for YouTube™, YouTube Music™, and Spotify. Processing stays on your device.",
  "permissions": [
    "activeTab",
    "scripting",
    "storage"
  ],
  "optional_host_permissions": [
    "https://open.spotify.com/*",
    "https://www.youtube.com/*",
    "https://music.youtube.com/*"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "assets/icon16-off.png",
      "48": "assets/icon48-off.png",
      "128": "assets/icon128-off.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_security_policy": {
    "extension_pages": "default-src 'self'"
  },
  "commands": {
    "toggle-effect": {
      "description": "Toggle last preset"
    },
    "toggle-slowed-reverb": {
      "description": "Toggle Slowed + Reverb preset"
    },
    "toggle-nightcore": {
      "description": "Toggle Nightcore preset"
    }
  },
  "icons": {
    "16": "assets/icon16.png",
    "48": "assets/icon48.png",
    "128": "assets/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "slowed-reverb@sahinozan",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}