Examine source code of Close Similar Tabs

{
  "applications": {
    "gecko": {
      "id": "CloseSimilarTabs@shuenyasui.com"
    }
  },
  "background": {
    "scripts": [
      "closeSimilarTabs.js"
    ]
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "96": "icons/icon96.png"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "description": "Close similar tabs with this lightweight and simple extension.",
  "manifest_version": 2,
  "name": "Close Similar Tabs",
  "version": "2.1",
  "permissions": [
    "tabs",
    "menus",
    "storage"
  ]
}