From MozillaZine Knowledge Base



RFC 3987 describes how IRIs (Internationalized Resource Identifiers) work. Mozilla implements IRIs in part by allowing IRIs to be converted to URIs. However, many websites break with this option enabled.

For compatibility with these websites, as well as parity with IE and Opera, Mozilla now treats the query portion of a URI (the part following the ?) differently than the rest. This preference controls whether Mozilla strictly follows RFC 3987, or uses the more widely-compatible conventions.

Possible values and their effects


Encode the query portion of IRIs as UTF-8.


Encode the query portion of IRIs using the same encoding as the current page. (Default)


  • Setting this preference to true may introduce encoding errors in pages you visit if the sites are not properly configured.

Recommended settings

If you commonly use websites that use “extended” (non-ASCII) characters in their URIs, you should probably leave this preference as false.

First checked in

2006-04-13 by Masatoshi Kimura

Has an effect in

  • Mozilla Firefox (trunk builds after 2006-04-13)
  • SeaMonkey (trunk builds after 2006-04-13)

Related bugs

Related preferences