Java applet can't open files under Safari 7 (Mac OS X 10.9)

Question

We have a web app that uses Java applet to manipulate files on local disk. We develop it for quite a while and we already know all types with issues an applet may have with

Answer 1

I had a similar problem with another Java app today. I think you may need to add your app to the "Allow the apps below ..." list in this dialog (System Prefs -> Security & Privacy -> Accessibility):