How can I get Firefox to use Dolphin instead of Nautilus by defalut?

Question

I installed Kubuntu, and want to use Dolphin when I try to save a file or open a new file, but firefox always use Nautilus, how can I change this?

I find this question, but it does not work for me: How can I get Firefox to use Dolphin instead of Nautilus?

I can neither download the kmozillahelper package, nor find the filepicker-variable in my firefox.

my Ubuntu: 12.10
my firefox: 16.0.2