Drag me
Drag me
Enable shim

On Firefox3/Win, the black DIV appears to obstruct the Flash SWF in the white DIV when you try to hover or click on the Flash SWF. The obstructed area appears to be any area on the white DIV overlapping an area of the black DIV except for the areas on the white DIV overlapping an area on the black DIV past the top-left offset of the white DIV. Bizarre!

This is illustrated in the example above. Any part of the white DIV not overlapping the black DIV is clickable. The area overlapping the black DIV surrounded by the red dashed border is also clickable.

I think this can best be explained by overflow auto/scroll creating some sort of chrome component, which somehow affects the mouse event region of Flash components. See: https://bugzilla.mozilla.org/show_bug.cgi?id=362193

FIXED: Using a fixed position shim fixed to (0, 0) with overflow set to auto and width/height both set to 100%. Note that the fixed position shim exhibits the same offset behavior as the absolute positioned DIV, but since we move it to (0, 0), it doesn't have any effect on the clickable area of the white DIV. Try dragging the black DIV to (0, 0) to visualize this.