Examine source code of Open Adjacent New Tab

{
  "manifest_version": 2,
  "name": "Open Adjacent New Tab",
  "description": "Opens a new tab adjacent to the current tab",
  "author": "Pranav Mangal",
  "version": "1.1.0",
  "homepage_url": "https://github.com/pranavmangal/firefox-open-adjacent-new-tab",
  "browser_specific_settings": {
    "gecko": {
      "id": "open-adjacent-new-tab@pranavmangal"
    }
  },
  "icons": {
    "48": "icons/adjacent-new-tab.svg",
    "96": "icons/adjacent-new-tab.svg"
  },
  "background": {
    "scripts": [
      "worker.js"
    ]
  },
  "commands": {
    "open-adjacent-new-tab": {
      "suggested_key": {
        "default": "Ctrl+Alt+T"
      },
      "description": "Open a new tab adjacent to the current tab"
    }
  },
  "browser_action": {
    "default_icon": {
      "32": "icons/copy-plus-black.png"
    },
    "default_area": "tabstrip",
    "default_title": "Open Adjacent New Tab",
    "theme_icons": [
      {
        "light": "icons/copy-plus-white.png",
        "dark": "icons/copy-plus-black.png",
        "size": 32
      }
    ]
  },
  "permissions": [
    "tabs"
  ]
}