When i'm using firefox , all the shadows come up great , but in some complex pages with heavy tables , it doesn't scroll right. If i keep scrolling down it works fine and scrolls pretty smoothly. But if i scroll up using the scroll-wheel or the scrollbar the whole firefox window gets corrupted with "clipping" bugs. This problem doesn't seem to occur in simple html pages. The same problem is visible in rdesktop (terminal services client) . if i try to move a window inside the main rdesktop window , the area within that window gets completely corrupted with clipping bugs.
When i posted this bug i was having nvidia-kernel drivers 61.11 . But just today i upgraded to the latest 66.xx nvidia-kernel drivers and i'm pleased to say almost all the problems i noticed are now gone. gkrellm2 and other odd shaped windows work mostly ok now. Just when i change to an odd shaped skin some of the sorrounding area gets corrupted but once i move the window around it is perfect. Even the nasty scrolling bug in firefox is now gone. The only problem i see now is the clipping bug in rdesktop. Who knows , its probably more xorg/nvidia driver related than xfce4wm related. All i can say is UPGRADE TO NVIDIA 66.xx DRIVERS NOW. Even the transparent windows are 20X faster to move around.
This sounds like it may be resolved. I'm reasonably sure this is an Xorg bug.
Unless proven innocent, I'm going to blame XOrg for this.