Examine source code of Back to Close WE

{
  "name": "Back to Close WE",
  "version": "0.7.2resigned1",
  "author": "Jasmin Bom",
  "manifest_version": 2,
  "description": "Use the back button to close newly opened tabs.",
  "icons": {
    "32": "icon.svg",
    "64": "icon.svg",
    "128": "icon.svg"
  },
  "permissions": [
    "tabs",
    "<all_urls>",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "options_ui": {
    "browser_style": true,
    "page": "options.html"
  },
  "applications": {
    "gecko": {
      "id": "back2close@bomjacob.github.io"
    }
  }
}