Examine source code of Quick Tab Counter

{
  "manifest_version": 2,
  "name": "Quick Tab Counter",
  "version": "1.0",
  "description": "Shows the number of open tabs instantly on the toolbar.",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Tab Counter",
    "default_icon": "icon.png"
  },
  "permissions": [
    "tabs"
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a8a49c9d-4894-4bc5-b8c2-2785a770f58a}"
    }
  }
}