A couple weeks back I got a response from MLB.com after a nasty email with a threat to demand a refund. Their rep explained to me that they were unable to make MLB.com work with Flip4Mac, but expected a fix soon (not happening yet). He also suggested using the old Windows Media Player for Mac, and explained settings that would allow me to hear my GameDay audio on Safari and FireFox. He also offered a refund I wanted it, but indicated MLB.com wasn't obligated to.
Well, I re-installed WMP, followed the settings suggestions, and got audio - the first time with Safari. But after that I've not been able to get it to work reliably - and never with FireFox. I found I had to change settings on the Flip4Mac Pref Panel (uncheck 'use as browser plug-in for audio'), but still it only works intermittently. I'm not sure if I should demand a refund still, but it's not totally broken. I'll futz with it a bit more and see.