Examine source code of Masked email extension

{
  "description": "Basic extension to create Fastmail masked emails on the fly",
  "manifest_version": 2,
  "name": "Masked email",
  "version": "0.3",
  "icons": {
    "32": "icons/fastmail.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "masked-email-extension@dxuuu.xyz"
    }
  },
  "browser_action": {
    "default_icon": {
      "32": "icons/fastmail.png"
    },
    "default_title": "Masked email",
    "default_popup": "popup/generate.html"
  },
  "options_ui": {
    "page": "options/options.html"
  },
  "permissions": [
    "storage"
  ]
}