Update: There is a new and very general solution available now. It works with Firefox and other GTK apps running in KDE. See the DK Bose's answer.
Original question:
I want to use KDE file dialogs (file open, file save) in Firefox in Kubuntu 12.04.
This requires something like the ancient KGtk script, but for KDE 4.x and recent Firefox versions.
OpenSuse offers this kind of functionality. Kubuntu dropped it, but surely someone has worked on bringing this back to Kubuntu (I hope).
Note, I'm not asking about theming/looks. I'm asking about actually using KDE file dialogs instead of XUL or GTK dialog.
And the preference ui.allow_platform_file_picker doesn't affect this. I have already tried setting it to true and false. Neither options results in using KDE dialogs.