It takes two to sync. Syncing another device with Firefox privately keeps your bookmarks, passwords and other Firefox data the same everywhere you use Firefox.
Ilaq ad ilin ssin i wemtawi. Amtawi n ufecku-nniḍen akked firefox ad yeḥrez ticraḍ n isebtar, awalen uffiren akked isefka-nniḍen n Firefox di yal taswiɛt d yal amkan deg ara tesqedceḍ Firefox.