Examine source code of Meomundo Close Tab Button

{
  "manifest_version": 3,
  "name": "Close Tab Button",
  "version": "1.2",
  "description": "Adds a button to the toolbar to close the current tab.",
  "icons": {
    "48": "images/CloseTabButton.svg",
    "96": "images/CloseTabButton.svg"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "action": {
    "default_icon": {
      "16": "images/CloseTabButton.svg",
      "32": "images/CloseTabButton.svg"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b1279102-6300-42a2-a35c-0151d805aa46}"
    }
  }
}