When I try to access CS50 Submit via Chrome (within the ApplianceI ) I get the big 403 "not allowed" page that others have mentioned. I can bypass this by using the link posted by Rob Bowden in another thread on this issue.
But when I click "Add Files" I do not get an "Open Files" window as the "How to Submit" section on pset1 says I should. Rather, I get a high-level summary of my hard drive contents from which I'm unable to access the contents of the Appliance.
I get the same results using both OS X v10.8.5 and Windows 7 Premium. I am enrolled in CS50 through edX.