If you're having trouble using the Folder Uploader on Box while using the Safari browser on your Mac, your Safari settings may be blocking the Java applet from running correctly.
Review the "Allow or block websites from using plug-ins" section of Apple's support documentation for detailed steps to enable the Java plug-in in Safari for Box.
Make sure you have Java installed and enabled in Safari. You can check to see that "Java" exists in Apple's System Preferences. If not, reinstall Java on your machine (you may need to work with your IT admin to ensure the correct version/installer for your environment is used).
Check your Java settings in Safari preferences:
Login to your Box account in Safari.
Choose Safari > Preferences, then click Security.
Make sure Enable JaveScript is checked.
Select the Websites tab
Find Java in the left-hand list under the Plug-ins section and make sure it is checked
In the list of Currently Open Websites or Configured Websites, look for yourcompany.app.box.com or app.box.com. It may also appear as yourcompany.ent.box.com
Press and hold the Option key on your keyboard, then select the Off drop-down and select Run in Safe Mode to disable it.
Click the Trust button when you see the popup dialog to trust "yourcompany.app.Box.com to run "Java" in unsafe mode." This setting is required to allow your files and folders to upload to your Box account.
Select the drop-down again and change Off to either On or Ask.
Click the done button and close the Websites dialog.
Now try Upload Folders again.
Click the Run button if you see "Do you want to run this application?" from Publisher: Box, Inc.