The "Undo arrow" becomes nearly invisible when using a darker Firefox skins. Could you fix this (or at least allow the user to choose a different color for the Undo arrow button) ? Other than that this is the extension I've been looking for in quite a long time.

P.S.: I also wished that the drop-down panel could look a little smoother and slicker than it does but that's up to the dev to tweak that or not.