FF Sync doesnt work by backing up your config directory to some cloud storage. That would be a recipe for disaster since your profile has certain machine specif

FF Sync doesnt work by backing up your config directory to some cloud storage. That would be a recipe for disaster since your profile has certain machine specific settings configured automatically by the browser. When you enable Sync you get to explicitly decide which things you want to include in the sync. I have mine set to just addons, configs, and bookmarks.