Force download instead of streaming of mp3 file in FF

Question

As the title says, I'd like to download a mp3-file instead of playing it in Firefox.

I do it like this:

<a href="http://test.com/path/to/my/file.mp3" download></html>

In all other browsers the file is downloaded, only Firefox starts playing the audio file instead of asking me if I would like to save it to my hard disk.