Examine source code of Tab List Button Enhanced

{
  "applications": {
    "gecko": {
      "id": "tablistbuttonenhanced@doub"
    }
  },
  "author": "ccDoub",
  "browser_action": {
    "browser_style": true,
    "default_icon": {
      "16": "icons/16-tabs.png",
      "24": "icons/24-tabs.png",
      "32": "icons/32-tabs.png",
      "48": "icons/48-tabs.png"
    },
    "default_popup": "popup/panel.html",
    "default_title": "Tab List"
  },
  "description": "Another button for tab lists with keyboard navigation, configurable buttons and a context menu for common actions.",
  "icons": {
    "16": "icons/16-tabs.png",
    "24": "icons/24-tabs.png",
    "32": "icons/32-tabs.png",
    "48": "icons/48-tabs.png"
  },
  "manifest_version": 2,
  "name": "Tab List Button Enhanced",
  "permissions": [
    "tabs",
    "storage",
    "bookmarks",
    "contextualIdentities",
    "cookies"
  ],
  "version": "3.0.0",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Ctrl+Shift+Y"
      }
    }
  },
  "options_ui": {
    "page": "options/options.html",
    "browser_style": true,
    "open_in_tab": false
  }
}