Examine source code of Tag Snag

{
  "name": "Tag Snag",
  "description": "Automatically snag all of your competitor's video tags on YouTube.",
  "version": "3.0",
  "manifest_version": 3,
  "browser_specific_settings": {
    "gecko": {
      "id": "admin@maxwellpepper.net"
    }
  },
  "author": "Maxwell Pepper",
  "icons": {
    "16": "images/icon16.png",
    "48": "images/icon48.png",
    "128": "images/icon128.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "scripting"
  ],
  "host_permissions": [
    "http://*/",
    "https://*/"
  ],
  "action": {
    "default_popup": "pop.html"
  }
}