Mozilla says that with Firefox Sync if you are working on one computer with 5 tabs open you can then switch to another computer or device and Sync can or will update the second computer with those tabs. How do I do this?

BACKGROUND
I have setup Firefox Sync on both devices and they have been synced. How do you sync them again? Is it automatically syncing them in the background? How often? How do you sync the tabs? Are the passwords synced?

Documentation
The documentation below describes how to add another device or computer to Sync. It says that when you add the device it syncs it. But it doesn't describe how and when it keeps it in sync or how to sync the tabs.
[1] http://support.mozilla.org/en-US/kb/what-firefox-sync