I had this problem with a iPhone 5S and a iPad Air. I solved this issue doing a complete restore to both equipments and configure like a new iPhone and like a new iPad.
Maybe I did things that are not necessary, but had tried many things and this is what solved my problem with iCloud Tabs.
This was the procedure that I did:
1- Go to Settings > iCloud and make sure that Safari is off in both equipments. Please make sure Safari stay desabilitado.
2- Disable Find My iPhone to both equipments.
2- Change the names to both equiment. Go to Settings > General > About
3- Restore both equipments
4- Configure like new equipments.
5- Now, after configure you Apple ID, active Safari in iCloud. (Go to Settings > iCloud) in to both equipments.
Now iCloud Tabs works fine.
Unfortunately I have to install all applications again, but your contacts and other things to sync with iCloud should appear again. Of course, they should be synchronized before.
Please, do a backup in iTunes before all this. If this procedure not work then you can use this backup and have your equipments exactly as they were before.