This add-on syncs all your tabs, bookmarks and history between your devices, also lets you share them between your friends. Also uses Dropbox and Google Drive as optional servers to save your tabs, bookmarks or history (Go to preferences to turn this option on).
The menu is located in Firefox browser's Tools.
You can turn off the auto-sync option if you want to but you can still choose what you want to save or not. You can view them from any device and any browser, not only Firefox! Share by introducing emails or by creating a group or with an existing group!
When you download the add-on, there is a help page, as well as a quickstart page that will guide you through the add-on.
You can also delete the saved items if you want to, you can stop sharing any item as well.
The mobile version is : Sync & Share Mobile version
Don't forget to add a review, even if it a bad one, it would be very helpful. Thank you!
Note: This add-on won't modify your bookmarks, history or tabs.