Examine source code of TubeMod

{
  "manifest_version": 3,
  "name": "TubeMod",
  "version": "1.15.1",
  "description": "TubeMod allows you to customize YouTube's UI to your preferences, by  keeping you focused on what matters!",
  "action": {
    "default_popup": "./public/popup.html"
  },
  "icons": {
    "16": "/icons/icon_16.png",
    "32": "/icons/icon_32.png",
    "48": "/icons/icon_48.png",
    "128": "/icons/icon_128.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "./scripts/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*",
        "*://m.youtube.com/*"
      ],
      "js": [
        "./scripts/content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "tubemod@extension.com"
    }
  }
}