Examine source code of BackTab

{
  "manifest_version": 3,
  "name": "BackTab",
  "version": "1.2",
  "description": "An extension that re-opens the previous page in a tab.",
  "browser_specific_settings": {
    "gecko": {
      "id": "{b9ba5cd8-6ebd-4442-a575-28aa596bd1bd}",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "16": "icons/icon-black-16.png",
    "32": "icons/icon-black-32.png",
    "48": "icons/icon-black-48.png",
    "128": "icons/icon-black-128.png"
  },
  "action": {
    "default_icon": {
      "16": "icons/icon-black-16.png",
      "32": "icons/icon-black-32.png",
      "48": "icons/icon-black-48.png",
      "128": "icons/icon-black-128.png"
    },
    "default_title": "BackTab",
    "theme_icons": [
      {
        "light": "icons/icon-white-16.png",
        "dark": "icons/icon-black-16.png",
        "size": 16
      },
      {
        "light": "icons/icon-white-32.png",
        "dark": "icons/icon-black-32.png",
        "size": 32
      },
      {
        "light": "icons/icon-white-48.png",
        "dark": "icons/icon-black-48.png",
        "size": 48
      },
      {
        "light": "icons/icon-white-128.png",
        "dark": "icons/icon-black-128.png",
        "size": 128
      }
    ]
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}