Is there a way to change this so it's legible
No, I'm afraid there is not, sorry, WB is not capable of changing font colors in those menus. So everyone is aware, Ive been over all of these issues time and time again and if something is illegible, chances are, there is not fix, in a truly dark skin.
Feel free to lobby Neil Banfield to get these unskinnable sections skinnable in future versions.
Firefox should be fine unless its an addon toolbar, in which case I obviously cannot vouch for every toolbar or menu addon. Standard firefox menus and toolbars should be perfectly fine.