Could not purchase gems on my new Macbook running 10.9.1. The window would come up blank no matter what I did. Decided to try it on my older Mac running 10.8.5 and it worked perfectly. Went back to the 10.9.1 machine right afterwards to see if the issue may have been solved some other way and the window was still blank on that machine.
Must be 10.9.1 then?