I assume you are setting tbody to display:block to make this work in Firefox and Chrome or have you found a new method?
The problem with setting tbody to display:block is that you lose the relationship between the data in the header and the data in the body unless you fix all the widths.
As far as I know having a scrollable tbody is not possible by simply addressing the tbody and without changing it to display:block. There seems to be no fix for IE either to make this compatible.
There are other CSS methods of having a fixed header and scrolling body but most have drawbacks which is why JS methods are still used for full cross browser support.