Examine source code of Media Blocker

{
  "manifest_version": 2,
  "name": "Social Media Blocker",
  "version": "1.0.0",
  "description": "Blocks X (Twitter), Instagram, and YouTube. Always on when installed — no options or toggle. Remove the extension to disable.",
  "browser_specific_settings": {
    "gecko": {
      "id": "social-media-blocker@media-block.local",
      "strict_min_version": "109.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Social Media Blocker - Custom block list"
  },
  "web_accessible_resources": [
    "blocked.html"
  ]
}