Examine source code of Forget Site

{
  "manifest_version": 2,
  "name": "Forget Site",
  "version": "1.0",
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "64": "icons/icon64.png",
    "128": "icons/icon128.png"
  },
  "browser_action": {
    "default_title": "Clear Site Data",
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png"
    }
  },
  "permissions": [
    "activeTab",
    "browsingData",
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "forget-site@example.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}