problem opening downloaded qxd file without extension in mac

I am trying to download QuarkXpress file without qxd extension using browser (firefox) in Mac (Tiger 10.4). This gets downloaded as a binary file and does not automatically open in QuarkXpress.

I dont have issues with downloaded files that have .qxd extension. However my client insists on automatically opening (without renaming) the files without extensions as well.

Any tips will be of great help. Thanks in advance.