This works for those who have both KDE and GNOME installed. I'm not sure if KDE installs GTK2 by default so you're on you own there and welcome to try.
You may have noticed that using apps like Firefox,Thunderbird, Gaim, Gimp, etc in KDE often gives very boring, flat and colorless backgrounds/widgets when used in KDE. This is because those apps are "Gnome centric" apps that use GTK2 (or in the case of Firefox/Thunderbird interact with it) to render those apps according to your theme settings in Gnome. When running them in KDE, it ignores all GTK 2 themes giving you that dull look. The fix for this is absurdly simply. If you happen to be one the many people who have both KDE and GNOME installed, you can fix it so that these apps display exactly as they would in GNOME, widgets and everything, while using KDE!
In your home directory, create a file named .gtkrc-2.0.
In that text file you want to add the following (here's an example with the theme I use)
gtk-font-name = "Comic Sans MS Bold 10"
include "/home/visceral/.themes/Glossy P/gtk-2.0/gtkrc"
The theme I use happens to be Glossy P, you just substitute what theme you want to use.
Save the file and re-log in KDE. You'll find that all your GTK2 apps now use whatever theme you specified in the .gtkrc-2.0 file. You can remove the Bold statement if you don't want that, and of course you can substitute what font you want in place of comic. It makes a huge difference for apps like Firefox, GIMP and Thunderbird. The best of both worlds.
I found this fix in a gentoo thread. I take no credit for discovering it, etc.
**There is nothing to download, just create the file and that's it. It's simply an improvement already available to make GTK2 apps look better in KDE.