Examine source code of StayFocused

{
  "manifest_version": 2,
  "name": "StayFocused",
  "description": "Block distractions, track usage, and stay productive with time limits and lockdown.",
  "version": "1.7.5",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "96": "icon/96.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "storage",
    "alarms",
    "tabs",
    "webNavigation",
    "notifications",
    "idle",
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "mohammad@anwar.app",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "StayFocused",
    "default_popup": "popup.html"
  },
  "options_ui": {
    "page": "options.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/custom-elements.js"
      ]
    }
  ]
}