Firefox Sync is Firefox’s synchronization feature that allows you to synchronize data such as bookmarks, passwords, open tabs and the history between multiple computer systems running Firefox. Up until now it has not been possible to synchronize add-ons using Firefox Sync. Users who wanted to use add-ons, and even more so their configuration, on multiple systems had to find other ways to keep the data in sync.

Plenty options are available to do that. Firefox users can make use of tools like Mozbackup or Firefox Environmental Backup Extension, use a service like Dropbox to host the Firefox profile in the cloud, or use the Siphon extension to synchronize add-on data.