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I only use FF , sync is Off.  I only use manual syncing with eversync.  The bug happened when I simply clicked "Start Synchronisation" in eversync. Of the 1129 bookmarks, only 59 were left on the computer and all the new bookmarks that were not on the server side were lost.  If I do it right now, it's fine, but this happened when I manually synced on 2 computers 3 days ago.  When it happened, it had been a while since the previous sync since I had not made change to the bookmarks in a while before that.