Examine source code of Side Panel localhost

{
  "manifest_version": 3,
  "name": "Side Panel 8080",
  "version": "1.5",
  "description": "Opens a side panel with localhost URL",
  "permissions": [
    "activeTab",
    "webNavigation"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "1024": "icons/firefox_extension_icon.png"
    }
  },
  "sidebar_action": {
    "default_panel": "panel.html",
    "default_icon": {
      "1024": "icons/firefox_extension_icon.png"
    }
  },
  "icons": {
    "1024": "icons/firefox_extension_icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{620f9189-b15f-4f59-b071-d06a93e8bd26}",
      "strict_min_version": "91.0"
    }
  }
}