How to change strange kde scrollbars?

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http://askubuntu.com – From a fresh Ubuntu 12.04 install I tried multiple desktops, and settled on KDE. One problem I have with it is how scrollbars are displayed in Thunderbird: In Gimp, Dolphin, Firefox there are completely normal scrollbars. I checked on unity and this didn't happen there. How do I change this? (HowTos)