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Protocols (ex: http, ftp, mailto) are different methods of sending information over the Internet. Protocols may be handled by Mozilla applications themselves, or they may be passed to external applications, or they may not be handled at all. On Linux and Mac systems, this preference determines whether a specific protocol should be handled at all (either internally or externally).

Possible values and their effects


This protocol should be handled either by the browser or by an external application.


This protocol should not be handled by the browser, nor by an external application.


  • network.protocol-handler.expose-all acts as an override to this preference. If network.protocol-handler.expose-all is true, this preference has no effect.
  • This preference has no effect on Windows. See this article for info.
  • This preference only exists by default for certain protocols.

First checked in

2003-11-20 by Darin Fisher

Has an effect in

  • Netscape (all versions since 8.1)
  • Mozilla Suite (all versions since 1.6)
  • Mozilla Firefox (all versions since 0.8)
  • Sunbird (all versions)

See also

Related bugs

Related preferences