Examine source code of Tab Counter

{
  "manifest_version": 2,
  "name": "Tab Counter",
  "version": "1.0",
  "description": "Displays the number of open tabs and allows closing duplicate tabs.",
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon.png"
    }
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{002fabe3-cbc9-4742-8f77-f3ca419f9770}"
    }
  }
}