The back/forward button's history drop-down indicator appears to always be disabled due to the gray color of it which seems to match exactly to the forward buttons disabled state color. Also, the button does not have any type of hover effect which adds to users not knowing that the button is active and also is used for both the back and forward buttons history. Even when active the button only gets a slight blue glow which is hard to see with the arrow being so small.

AFAIK the dropdown indicator is going to be removed, so I suppose this bug should be INVALID. Although one could check, if we need such highlighting for other dropdowns.