How do I push new sync data or remove bad data on all my devices?
Every time I delete my browsing history or remove a bookmark from any of my synced devices, the other devices re-sync it right back again. How do I get *ALL* my devices to reflect new sync data, and to reflect deleted sync data? The old Sync offered me an option to replace all devices data with a new device's sync data. I can't find anything similar in the new sync.
Alla svar (1)
AFAICT, new Sync keeps sending in data but is highly unwilling to erase it (can't tell new from old). New Sync's data transfer operations are still hidden from user access, too: https://bugzilla.mozilla.org/show_bug.cgi?id=966530.
What this means is that you can do very little via the UI. Basically you'll have to do things manually for now; the fastest way to erase server-side data is to change your password: https://support.mozilla.org/en-US/questions/1069771.
I stopped using Sync because it is currently more hassle for me than it is worth. Might be a while before it's on par with the better solutions out there.