Examine source code of Tab Clock

{
  "manifest_version": 2,
  "name": "Tab Clock",
  "version": "1.2.2",
  "description": "Monitor active browsing time per open tab",
  "browser_specific_settings": {
    "gecko": {
      "id": "{cc143415-9777-4c5a-84b2-fc9db1cf58ba}",
      "strict_min_version": "96.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "16": "png/16.png",
    "32": "png/32.png",
    "48": "png/48.png",
    "96": "png/96.png",
    "128": "png/128.png"
  },
  "browser_action": {
    "default_popup": "html/popup.html",
    "default_icon": {
      "16": "png/16.png",
      "32": "png/32.png",
      "48": "png/48.png",
      "96": "png/96.png",
      "128": "png/128.png"
    }
  },
  "background": {
    "scripts": [
      "task/bg.js"
    ]
  },
  "permissions": [
    "tabs"
  ]
}