Been waiting for a tool like this for a long time!

Google Browser Sync for Firefox is an extension that continuously synchronizes your browser settings – including bookmarks, history, persistent cookies, and saved passwords – across your computers. It also allows you to restore open tabs and windows across different machines and browser sessions.

Google Browser Sync is completely automated. The settings you select at startup are automatically synchronized across each of the computers on which you install Browser Sync. You won’t even need to log in every time you start the browser. You can change which browser components are being synced – or even stop the syncing process entirely – using the settings panel in the upper-right corner of the page. The settings panel also gives you access to your PIN.

Google Browser Sync