RDF not recognized

Why is it that even this code doesn't works on firefox?


<?xml version="1.0" encoding="utf-8"?>
<RDF:RDF xmlns:RDF="http://www.w3.org/1999/02/22-RDF-syntax-ns#">

  <RDF:Description RDF:about="http://www.search.net/mammals/lion">
    <ns1:name xmlns:ns1="http://www.search.net/RDF#">Lion</ns1:name>
  </RDF:Description>

  <RDF:Description RDF:about="http://www.search.net/mammals/hippopotamus">
    <ns2:name xmlns:ns2="http://www.search.net/RDF#">Hippopotamus</ns2:name>
  </RDF:Description>

  <RDF:Description RDF:about="http://www.search.net/mammal/horse">
    <ns3:name xmlns:ns3="http://www.search.net/RDF#">horse</ns3:name>
  </RDF:Description>

  <RDF:Seq RDF:about="http://www.search.net/main-search">
    <RDF:li RDF:resource="http://www.search.net/mammals"/>
  </RDF:Seq>

  <RDF:Seq RDF:about="http://www.search.net/mammals">
    <ns0:name xmlns:ns0="http://www.search.net/RDF#">Mammals</ns0:name>
    <RDF:li RDF:resource="http://www.search.net/mammals/lion"/>
    <RDF:li RDF:resource="http://www.search.net/mammals/hippopotamus"/>
  </RDF:Seq>

</RDF:RDF>


regards.
pablo.