I also got the firefox for android after seeing the sync feature. However the tabs don't sync by default and I haven't seen any guide on how to use this feature. I'd appreciate any pointer in the right direction.
On the desktop (in Firefox 57), you can find your tabs under Library->Synced Tabs.
On the Android version, they appear on the homepage->History->Synced Devices.
Mind that they don't sync immediately. There's an interval for syncing. You can lower this interval in about:config by editing one of services.sync.scheduler.*, also possibly services.sync.syncInterval, but I don't know for sure what each individual one does. Also, you can tell it to do a sync right away, on the desktop version with Alt+t, then s; on the Android version by going into the settings, then tapping on "Firefox Account" at the top and then "Synchronize now".
