Examine source code of Tab Counter Badge

{
  "manifest_version": 2,
  "name": "Tab Counter Badge",
  "version": "1.0",
  "description": "Displays the number of open tabs directly on the browser icon.",
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_title": "Tab Counter Badge",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png",
    "128": "icon.png"
  },
  "applications": {
    "gecko": {
      "id": "tabcounterbadge@example.com",
      "strict_min_version": "60.0"
    }
  }
}