In the last release, Firefox introduced a new Sync version, the feature with which you can synchronize your passwords, history, addons etc. For more information on Sync, go here: http://www.mozilla.org/en-US/firefox/sync/

However, when I migrated just today, I can’t tell you how disappointed I am given that:

• You can NOT sync you passwords if you have a master password (which, in my standpoint, is necessary to have) (Link to the documentation stating this)
• You can NOT roll back to the old Sync feature (on Firefox 29) (or not that I know of)

So here I am, stuck with the new Sync on one of my devices, with no way to sync my passwords except if I chose to store them insecurely on my computer. That’s just great, especially because synchronizing passwords was the number one reason I used Sync (as I have a unique password per website). My only advice: don’t migrate to the new Sync (yet).