Firefox 11 will Synchronize Add-ons
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 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.
All of this may soon be a thing of the past. Mozilla aims to integrate add-on syncing into Firefox 11. All Firefox users who use Firefox Sync can then synchronize all installed add-ons across all their computer systems.
It is however not possible to sync add-ons between desktop and mobile Firefox installations and only add-ons hosted at Mozilla's official add-on repository can be synchronized this way.
Users with third party add-ons, for instance from security suites who install add-ons into the browser, need to find other ways to synchronize those between the browsers.
It is also interesting to note that all add-ons, regardless of their activation status, will be synchronized by Firefox Sync. The activation status refers to the state of the add-on, whether it is enabled or disabled in the browser.
The add-ons will retain their activation status on the target computer. There is no functionality at this time to synchronize only selected add-ons between devices.
Existing sync users won't have the new feature enabled by default. They need to enable add-on syncing in the Firefox Sync preferences to enable it.
This is done with a click on the Firefox button, the selection of Options, and a click on the Sync tab in the opening preferences window. New Firefox Sync users will have add-on synchronization enabled by default.