If Firefox 2.0 does not recognise a mime-type it forces you to jump through hoops every time you wish to save a file of that type – never giving you the option to make a default action (eg. save-as) for the type.
Getting tired of this I eventually did some research to find a solution, case in point is the RAR file type (application/x-rar; application/x-rar-compressed).
Option 1: An Addon
Add the Mime-Edit extension that allows you edit any mime-type’s properties and actions, even those not recognised by Firefox.
Option 2: Hack
If you are confident in XML manually edit mimeTypes.rdf in your profile folder:
<RDF:Description RDF:about="urn:mimetype:application/x-rar-compressed" NC:fileExtensions="rar" NC:description="" NC:value="application/x-rar-compressed" NC:editable="true"> <NC:handlerProp RDF:resource="urn:mimetype:handler:application/x-rar-compressed"/> </RDF:Description> <RDF:Description RDF:about="urn:mimetype:handler:application/x-rar-compressed" NC:alwaysAsk="false" NC:useSystemDefault="false" NC:saveToDisk="true"> <NC:externalApplication RDF:resource="urn:mimetype:externalApplication:application/x-rar-compressed"/> </RDF:Description>
And in the section <RDF:Seq RDF:about=”urn:mimetypes:root”> add in this new row:
<RDF:li RDF:resource="urn:mimetype:application/x-rar-compressed"/>