I've tried the following in safari 6.1.6 on 10.8.5 as well as the latest webkit nightly r173508. I've set up two samples. In the first the overflowing pseudo element part (blue) should be hidden
while in the second the overflowing part of the grey div should be hidden.
In both cases if you click with the mouse and keep it clicked and move it to the right the page is scrolled horizontally and the initially hidden overflow is shown. The overflow on the right side for the red pseudo element is hidden properly and impossible to scroll. But on the right webkit is ignoring the overflow-x property completely. The first pen is tested in:
Safari: not working
Webkit nightly: not working
Chrome: not working
Opera: not working
opera next: not working
Firefox: working as expected.
I don't see any difference in rendering between a current nightly and Firefox 32.
(In reply to comment #1)
> I don't see any difference in rendering between a current nightly and Firefox 32.
I've created brief screencasts for each browser showing the issue:
all created with the following pen: http://codepen.io/rpkoller/pen/buAHm