Fix Firefox 3 mimeTypes to save rar files

close Firefox
add this to mimeTypes.rdf in your %userprofile%\Application Data\Mozilla\Firefox\Profiles

<RDF:Description RDF:about="urn:mimetype:application/zip"
NC:value="application/zip"
NC:editable="true"
NC:fileExtensions="rar"
NC:description="WinRAR ZIP archive">
<NC:handlerProp RDF:resource="urn:mimetype:handler:application/zip"/>
</RDF:Description>

save, open firefox, test it