We recommend Chrome or Firefox, but if you have to stick with Safari and you are having problems you should check to see if you have Flash installed. If you don’t, you need to install the Flash plugin.
If you continue to experience problems after installing the Flash plugin, you may want to clear your Flash settings. You can do this as follows:
System Preferences –> Flash Player –> Storage tab –> Delete All –> Delete All Site Data and Settings checkbox –> Delete Data button.