Using Firefox 8.0.1, all the on-screen buttons for ALL sites have disappeared.
Not the toolbar buttons, but the buttons like NEXT, BACK, CONTINUE, PAY, GO TO BASKET and CONTACT US that should appear in various parts of the screen on the web pages.
Sometimes they are still visible (and clickable) as text, but in other cases they have disappeared entirely, although a click symbol still appears if you can guess where they are and mouse over them.
Where have they gone? How can I restore them back?