There should be a toggle to show implicitly set properties in the computed style pane. Right now only properties that the combined matched rules apply are shown. This is a good default, since it shows you the relevant properties, but sometimes you need to see all properties that are currently applied or inherited.
Created attachment 15219 [details] Patch
Comment on attachment 15219 [details] Patch r=me
Landed in r23764.
Another fix was landed in r23790 to make sure the setting was remembered between nodes.