I'm not finding anything for configuring KDE4 themes. I think your best bet is to ask on the
KDE Forum. Themes for Firefox are easier. The hardest part is deciding which one to use. Just go to the
Firefox addons site, enter the term
theme in the search bar and wait for the results. If you have not yet upgraded to Firefox version 10 as a Synaptic update, I'd hold off on installing any themes until after the upgrade.