They show up in Safari on my iOS devices (two ipads and iphone) and my iMac at home. But they don't on my work Macbook Air. When I click on the iCloud tabs icon it a popup box comes up with the icloud logo and the message : icloud automatically shows all the open tabs on your other devices.
iCloud is on on the macbook air, and Safari is chosen in the list.
iCloud is on on the macbook air, and Safari is chosen in the list.