Examine source code of Site Time Tracker12

{
  "manifest_version": 2,
  "name": "Site Time Tracker",
  "version": "1.0",
  "description": "Track time spent on each website, local-only, no login required.",
  "permissions": [
    "tabs",
    "storage",
    "webNavigation"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_title": "Site Time Tracker"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{29d1b13c-1230-4dee-b185-dc3e830fbd2a}"
    }
  }
}