Safe Mode is the default user mode in Safari 6.1 or later, but it can prevent content files from being uploaded in Mindflash.
When an Administrators goes to the Arrange window in Safari, Safe Mode prevents content files from being uploaded when "Insert +" button is clicked. When the "Insert +" button is clicked, the window to select your files does not appear. Safe mode blocks this.
In order to be able to upload your content files in Safari, Safe Mode will have to be disabled for Mindflash website. The article link below, from Adobe Flash, details the steps to disable Safe Mode.