They have a countdown on the Muoversi a Firenze site:
(Please note the above is a static image from late Friday night - the Tram goes live Sunday morning the 14th of Feb.)
Unfortunately the site is in Italian only - but the short story is that the Tramvia (Line 1) is set to go live on Sunday morning at 6:30 AM. The downside is that this will mean a lot of other changes to traffic patterns, bus routes and stops, etc. If you are coming to Florence or are a resident, you need to get acquainted with these changes! You can also check the ATAF website for news and details on the bus changes (I notice the ATAF site has been updated and seems much more useful now also - good news).