Examine source code of SiteSeal

{
  "name": "SiteSeal",
  "version": "1.0",
  "description": "Block all cross-site requests using the WebRequest API to enhance your browsing privacy and prevent unwanted tracking across the web",
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "{490454b5-b6b5-4205-82fc-99b10e7de6a2}"
    }
  }
}