Examine source code of Decode On Copy

{
  "manifest_version": 2,
  "name": "Decode On Copy",
  "description": "Automatically base64 decodes any text copied to the clipboard if that text can be decoded to a valid URL.",
  "version": "1.1resigned1",
  "applications": {
    "gecko": {
      "id": "decodeandcopy@decodeandcopy.com"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "index.js"
      ]
    }
  ],
  "permissions": [
    "activeTab",
    "clipboardWrite"
  ],
  "icons": {
    "16": "icons/icon-16.png",
    "19": "icons/icon-19.png",
    "38": "icons/icon-38.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  }
}