When I am logged in to my Firefox account always and all the settings are ON - bookmarks, passwords and all, why I cannot restore them after I have reinstalled my WIN 10??? Earlier it used to synch all the items, but as the newer versions are coming, I guess all these features are one by one removed! What a waste!

This has happened because my HDD had crashed yesterday. Fortunately I had manually exported all my tons of bookmarks sometimes back, which saved my @$$!

Sync is not meant as a backup. It is meant to share data.

Sometimes under your situation, when you log back into sync, the sync servers may think you had removed the data and removed the same from the servers.