The properties pane should show all the DOM properties that are exposed to javaScript and ObjC. Like offsetTop, parentNode, attributes, etc. Properties like attributes should be a a collapsable tree that shows the sub-items. some features here could include (double)clicking to jump to the parentNode, or firstChild.
This pane has a rough first cut as part of Bug 10163.
The properties pane should show the prototype chain, to make things easier to view.
This was fixed when the new inspector landed in r23677