Examine source code of Time counter on tab

{
  "manifest_version": 2,
  "name": "Tab Timer",
  "version": "1.0",
  "description": "Tracks how long you spend on each tab during a browsing session.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6c052b79-4104-4be2-90a2-91c0f5e5cf9b}"
    }
  }
}