Examine source code of Website Blocker

{
  "manifest_version": 2,
  "name": "Website Blocker",
  "version": "1.0",
  "description": "Block access to specific websites",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{cc76e828-cbd1-4edd-a88e-764bc2bd8846}"
    }
  }
}