Examine source code of Improved Tab Manager

{
  "manifest_version": 2,
  "name": "Improved Tab Manager",
  "version": "2.3.4",
  "description": "Enhance your Firefox with Improved Tab Manager",
  "browser_specific_settings": {
    "gecko": {
      "id": "improved-tab-manager-2f4gskrh@firefox.extension",
      "strict_min_version": "101.0"
    }
  },
  "permissions": [
    "tabs",
    "storage",
    "webNavigation",
    "history",
    "contextMenus"
  ],
  "browser_action": {
    "default_icon": {
      "16": "icons/icon-16.png",
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    },
    "default_title": "Improved Tab Manager",
    "default_popup": "popup/popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "16": "icons/icon-16.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "developer": {
    "name": "Anonymous",
    "url": "https://example.com/improved-tab-manager"
  },
  "homepage_url": "https://example.com/improved-tab-manager"
}