Restore XFCE to default

[gold_finger]

Can't help with Mate, but you can add/delete/change panels and items on the panels by right-clicking on an empty area of the panel, choose -- Panel -> Panel Preferences -> Panel 1 or 2 -> "x" to delete it, or "+" to add a panel.  You can have a look through the tabs -- Display, Appearance, Items -- to customize it however you want.  To move a panel, look under Display tab and uncheck the "Lock panel" box; then grab by the left or right panel edge and move it.