When Netflix added Starz Play they also included the Starz Live streaming channel, a first for Netflix. It's not easy to find, but there is a link on the right side of the Starz Play page (or you can bookmark http://www.netflix.com/StarzLive.
You can see the schedule on the Starz website: http://www.starz.com/schedule.
The Starz Play titles work on the Macintosh and in Firefox, the Starz Live channel gives an error on the Mac or Firefox.
Your system does not meet the compatibility requirements for the Starz TV channel.
Update: A Netflix spokesperson says that Starz Live will work on Firefox and Intel Macs by the end of the year.
Thanks to Manny for sending this in.