This is a follow up bug for polishing about:sessionrestore in Firefox (bug 459950). Currently XUL trees use a black and white gif image of a check in columns that have the attribute type="checkbox" The purpose of this bug is to propose switching to the native checkbox appearance on each platform.
This is not really easy. Trees are dumb. If we don't want to use images, we need to teach trees how to use -moz-appearance for the ::-moz-tree-image pseudo element. And then we must make sure that the cell's state (checked, focused, mousedown) is passed to the theme drawing code correctly - this is a similar problem as in bug 301060. Furthermore, trees currently don't keep track of the mousedown state, so this must be added, too.
about:sessionrestore could make use of bug 405913 or bug 367843 (not sure if there's a difference between these bugs).