Network.IDN show punycode

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IDN support allows users to enter domain names containing extended characters that aren’t supported in “standard” URLs. This makes it possible for international websites to register domain names using characters native to local languages.

In order to expand the number of characters allowable in domain names to include all Unicode characters, a type of encoding called “Punycode” was developed. This encoding uses legal characters in domain names—dashes, letters, and numbers—to represent Unicode characters. When IDN support is enabled, Mozilla recognizes domain names encoded this way and converts them into Unicode strings. Thus, a domain name that looks like is converted into a domain name that looks like http://tūdaliņ.lv.

Mozilla’s initial response to phishing attacks using IDNs (after disabling IDNs entirely) was to display the punycode form of IDN URLs.

This preference determines whether all IDNs displayed in the browser are displayed as punycode or as Unicode.

Possible values and their effects


Display the “raw”, punycode version of internationalized domain names.


Display IDNs as intended. (Default)


  • IDN must be enabled for this preference to have an effect.
  • Even if this preference is false, only top-level domain that are whitelisted will be displayed in Unicode.

First checked in

2005-02-17 by Darin Fisher

Has an effect in

  • Deer Park (all versions)
  • Mozilla Firefox (all versions since 1.5b1)
  • SeaMonkey

Related bugs

Related preferences

External links