Using Upfront on what browser?

I dont know what I'm doing wrong but it seems a lot of the functionality of upfront it not working on my end. Firefox 43.0.4 seems to not not work properly it asks me if I want to stop running an unresponsive script. Safari 9.0.3 and every browser I have tried doesn't allow me to alter the color of icons using the method described in the tutorial. Do you have other sources on how Upfront works? What is available is really short and assumes a lot for the user. I am also using a Mac. What is the ideal system to be running upfront?