User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0
Steps to reproduce:
Setup Sync with all of your devices.
My password and library were synced (including "tabs" in a deep sub-menu).
I would expect my actual tabs to sync (if I open or close a tab on any device, it should do the same on all other devices), since tabs are one of the main features that warrant syncing.