Glad they are supporting it! Looks like that page is just to download one. I wish they would add Chrome to it but meh. Not a big deal. Google has advertising all over for Chrome it seems when you use IE, maybe on the other ones also.
This is odd ... but it's not like Google doesn't do the same thing all the time, at least to a degree.
Look at its most recent interactive Google Doodle, the Moog keyboard. When you accessed the page on Firefox, there was a little note that said something like, "Consider upgrading to a modern browser like Chrome to get the full experience." (I think the Chrome version made use of a different method for producing the audio -- presumably implemented for the sole reason of promoting Chrome.)
It's always been on there.