I saw this on Gizmodo. I haven't used, or tried to use, One to One and don't plan to anytime soon, but I do own an iPhone 4S, new iPad, and a MacBook Pro.
I'm going to start by saying this is completely unacceptable, there is no technical reason to not allow Chrome. This is unnecessary and just plain stupid behavior! I don't know if this was a company decision, or somebody's individual screw up, but it needs to be resolved.
I buy Apple products because I expect things to "just work", and I use Chrome because it has Flash preinstalled and I don't want to install it individually, which is completely irrelevent - I choose to use Chrome on my Mac, it shouldn't matter. This is 100% counterintuitive to the "just works" ideology. There is NO technical reason to not allow other browsers other than Safari - none.
Which version of Firefox are you using?
I was able to schedule (and cancel) a one-one-one reservation using Firefox 14 (14.0.1) on Windows 7. I'm not in a position at the moment where I can test in OS X.
If you are still using and old version (i.e. 3.6) then I can understand Apple complaining about it. The download "Safari" comment isn't really a big deal or any different than when Google says "blah runs faster with Chrome... download now."