I am recognizing more things being off on the color than just Firefox menus.
The system tray has many things off. The tray itself is white rather than grey that I have on my F21-x86-Xfce notebook. The NetworkManager icon is black fill rather than grey (or is it off-blue?).
The Trash desktop icon is white/grey rather than shades of blue.
I looked on Setting > Appearance and everything is set the same as on my notebook.
Oh, and no Sensor plugin in Xfce.