Examine source code of Browse Timer

{
  "manifest_version": 2,
  "name": "Browse Timer",
  "version": "1.0",
  "description": "Track time spent on each website.",
  "permissions": [
    "tabs",
    "storage",
    "activeTab",
    "notifications"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "timetracker.png"
  },
  "homepage_url": "https://github.com/Euuiiii/TimeTracker",
  "author": "Time Tracker Team",
  "browser_specific_settings": {
    "gecko": {
      "id": "{934257d2-858d-4229-8ff4-5315c094eb25}"
    }
  }
}