The very first thing I was greeted with on the "top sites" page was a bunch of "Recommended by Pocket" links, and no way to disable that.
I can't find anything in about:config to disable this either. How about NO, goddammit?
Shame on you, Mozilla.
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".
Hamburger -> General -> Home -> Top Sites
Then it can be toggled off. Whew!
EDIT: It's still not nice to have this sort of thing come up by surprise.