Comment 35 for bug 422511

The way gtk is handling trough-border is technically correct, but it is incorrect from a usability viewpoint. One way to fix it is to change gtk's handling of trough-border. I did that, but Firefox needs to be fixed separately because it does its own UI drawing and handling.
The other way is to fake the effect, and set the gtk trough-border to 0. Some themes do this by using the pixbuf engine for the scrollbars (e.g. Dust). I patched murrine to simply draw a thinner scrollbar handle (configurable using a murrine engine parameter) to get the same effect. All the while gtk thinks the trough-border is set to 0, so it avoids all the problems (and it doesn't affect sliders). This fix is a bit of a hack, but I've been using it and didn't have any problems.
This is the murrine patch: http://launchpadlibrarian.net/34046350/murrine_trough_border_proper.patch.
I've also attached the changes to gtkrc that are needed to get the same effect with the murrine patch.
IMHO the murrine patch is better than reworking the way gtk handles trough border.