I’m not an expert on that but I think it does not open not because it is an unsupported browser as stated on the page but because of ActiveX controls.
Web sites that depend on ActiveX will not work with Firefox. There are two sides to this coin. The lack of ActiveX support is part of what makes Firefox safer than Internet Explorer. On the other hand, it means you must use IE for some very useful web sites.
That’s what I find elsewhere.
Anyway I don’t think they need these ActiveX controls to run the flash casinos. I found a lot of casinos working perfectly with firefox. They should be aware of this since Firefox is growing in use, and change the software for cross compatibility.
Maybe it’s time to all of us to care about this and do something.