The modern theme has an abundance of complicated XBL and CSS arrangements that we should be able to simplify. In some cases this may require graphical compromises, in other cases it may not. Bug 112980 describes some changes to the theme architecture that may allow these simplifications to happen. For instance, many of our 9-slice widgets (buttons, urlbar, menulists) can be reduced to a single "slice" by using multi-level CSS borders and gradients. The primary toolbar is also a big target of mine, as it uses slices for the left and right ends, and has a stack in there as well.