quote from - http://www.tuxradar.com/content/20-all-new-tips-kde-42
#12: Make GTK apps look like KDE ones
To get Gnome applications to look like their KDE counterparts involves installing a package called gtk-qt-engine, and both Kubuntu and Mandriva offer official packages. After installation, you'll find an extra configuration page in the System Settings/Appearance window called 'GTK Styles and Fonts'. Click on this, and you have several options on how to bring the two styles together.
Firstly, click on 'Use My KDE Style In GTK Applications' and make sure 'Use KDE fonts' is also selected. Then click on the 'Install Scrollbar Fix' to make an alteration to your Mozilla profile that should make the scrollbars in Firefox and Thunderbird look identical to those on native-KDE applications. You need to restart KDE to apply the changes, and you should see that the colours, icons and fonts have changed, as well as window decorations like the scrollbars.
So far I'm loving Salix.