ActiveWidgets broken in Mozilla 1.8a4

Both on my site, and in the example grid on the front page of activewidgets.com. The header row cells all have horizontal scrollbars obscuring the text. Each data row also has an obscuring horizontal scrollbar, which disappears if all columns are made to fit within the containing div. The JavaScript console complains about unknown properties text-overflow, xvertical-align, and box-sizing.

Displays properly in Mozilla 1.8a2 and FireFox. I have not downloaded the Mozilla nightly to see what it does