Examine source code of Clear Cookie is

{
  "manifest_version": 2,
  "name": "Clear Cookies for Current Site",
  "version": "1.0",
  "description": "Clear all cookies for the current website with one click.",
  "permissions": [
    "cookies",
    "activeTab",
    "tabs",
    "<all_urls>"
  ],
  "browser_action": {
    "default_icon": {
      "16": "icon.png"
    },
    "default_title": "Clear Cookies",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{285a3045-dad5-43af-b2d6-5ad0221e2abe}"
    }
  }
}