I use KDE as my primary desktop environment. I also have GNOME and Xfce installed along side. As a result (I think), different applications use different file manager for desktop integration. Dropbox uses Nautilus. Ubuntu One uses Nautilus. Firefox uses Thunar (when you click on the downloads to show the directory). How do I make them use Dolphin instead?
I guess You can set dolphin as default file manager with
I would also check KDE setting: System settings -> Default applications -> File manager
Finally I think dropbox won't respect the setting, because it integrates with nautilus only.