Safari should be working (although it looked to me like mouse/touch events weren’t detected so we’ll need to look into that).
IE11 turns out to be a complete mess. We’re working to support it (probably in 3.0.0b7 sometime next week?) but, when we do, I would very strongly recommend that you use a better browser! Performance under IE11 will definitely be worse than almost any other option.
Firefox or Chrome are very much superior and work everywhere.