Examine source code of Tab Counter Badge

{
  "manifest_version": 2,
  "name": "Tab Counter Badge",
  "version": "1.0.0",
  "description": "Display the number of open tabs as a badge.",
  "icons": {
    "48": "icons/icon.svg"
  },
  "browser_action": {},
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "tabcounter-8a9c4a91289f@local",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  }
}