Examine source code of Time Tracker

{
  "manifest_version": 2,
  "name": "Time Tracker",
  "version": "1.1",
  "description": "Track how long each tab is active",
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7930e9e1-4a45-4ea1-875c-112453bcf1af}",
      "strict_min_version": "110.0"
    }
  }
}