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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. This preference determines whether Mozilla will parse and load IDNs.

Possible values and their effects


Parse and try to resolve internationalized domain names entered in the Location Bar and in links. (Default)


Do not parse or resolve IDNs.


  • Past versions of Mozilla products have had security issues with the built-in IDN support. Specifically, a type of website spoofing attack and a heap overrun attack due to a parser bug. In both cases, IDN support was temporarily disabled with this preference until a better solution was developed.
  • IDN support is limited to a subset of all top-level domains, enumerated in preferences.
  • Certain characters that are technically legal in IDNs are blacklisted, and cause the domain name to be shown as punycode.

First checked in

2002-03-05 by Darin Fisher

Has an effect in

  • Netscape (all versions since 7.0)
  • Mozilla Suite (all versions since 0.9.9)
  • Mozilla Phoenix (all versions)
  • Mozilla Firebird (all versions)
  • Mozilla Firefox (all versions)
  • SeaMonkey (all versions)

Related bugs

Related preferences

External links