Mmm, it seems there's something wrong on our UI that makes unusable that part of the UI.
Having said that, don't use the same user as the one you created during installation. And if you create a directory in your file system, you will have to set the permissions properly with chmod/chown. Sorry the part that doesn't work from your UI is the one that did that job for you.
Could you please tell me what firefox version -any relevant addon?- and OS you are using to connect to the web interface?
Thanks