The good folks at KDE have devised an apparently simple way to allow GTK apps to integrate into KDE to the point of using KDE file and print dialogs. There's some documentation on this at http://developer.kde.org/documentation/tutorials/qtgtk/main.html and the sources are available from ftp://ftp.kde.org/pub/kde/unstable/apps/KDE3.x/utils/qtgtk-0.1.0.tar.gz ftp://ftp.kde.org/pub/kde/unstable/apps/KDE3.x/utils/qtgtk-0.1.0.tar.bz2 or more generally ftp://ftp.kde.org/pub/kde/unstable/apps/ and then nav through the latest KDE dir to the utils dir. Combined with the QT-GTK theme for GTK apps there's a good possibility of getting Firefox to resemble and work like a native KDE app. http://www.kde-look.org/content/show.php?content=9714 I must admit that I don't hold out much hope on this given the disposal of the earlier QT port for Mozilla but this isn't nearly as ambitious.
I don't see why this request is particular to Firefox -- could not the same technology be used to integrate Mozilla into KDE as well? If so, perhaps the original poster could change the "Product" field to "Core".