Go to Administration, Permissions. Click the link for Roles than can browse and upload but only in a user specific folder, and make sure that the box is checked by the user role(s) you want to apply this behavior to. If you want to apply this to everyone, select the Authenticated Users role.
Next, go to Roles that can browse and upload files, and make sure that the roles you checked above are not checked here. This may be precautionary--I'm not sure offhand how mojoPortal would handle it if it a role were checked in both places.