Examine source code of Nuxify

{
  "manifest_version": 3,
  "name": "Nuxify",
  "description": "Takes every Youtube video starting with \"I\", replaces it with \"we\", and adds Nux Taku in the thumbnail",
  "version": "0.3.3",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "64": "icon/64.png",
    "128": "icon/128.png",
    "256": "icon/256.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "nuxify@gducrash",
      "strict_min_version": "60.0"
    }
  },
  "permissions": [
    "storage"
  ],
  "web_accessible_resources": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "resources": [
        "media/*",
        "audio/*"
      ]
    }
  ],
  "action": {
    "default_title": "Document",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*",
        "*://youtube.com/*"
      ],
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}