There are usually fixes for this but they are not always simple to implement. This is a concept call stacking order, which has a CSS tag z-index. Like layers in Photoshop, where you have multiple objects residing in the same space and you have to indicate which one gets displayed on top of the others.
That part is simple to grasp. The complication is in CSS the layers being addressed have to be part of the same positioning context, meaning there must be an ancestor element to both elements that has position: relative set on it.
I see you already have some z-index settings in your CSS. What needs to happen is #tabs ul li li must have a higher z-index than #tabs ul li Right now #tabs ul li has a z-index of 1000, and by inheritance, so does #ul li li
I tried increasing the z-index of ul li li in Firebug but that did not
I find this is one of the most confusing areas in CSS.