scrollbars are inactive but the mouse scroll is active

Hi Everybody,

I am seeing a funny behavior in the grid, which has 74 rows and 8 columns.
I dynamically decide the width of my columns and add rules to stylesheet., along with the
following rules
.active-grid-column {border-right:1px solid threedshadow;}
.active-grid-row {border-bottom:1px solid threedlightshadow;}
.active-scroll-bars { overflow:scroll}

I do see a horizontal and a vertical scrollbar, but they are inactive, while the mousescrolling
works for vertical scrolling. How do I activate my scrollbars ? I am seeing this behavior in mozilla
[Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.1) Gecko/20021003].

Any help is greatly appreciated.
Thanks!
-A.