With Browser Security Plus' Download Restriction feature, you can limit downloads to trusted/authorized websites. This can be achieved in two ways:
You can choose to limit downloads from specific authorised websites if you want to implement a lockdown. This will ensure that users can not download from websites that aren't trusted
You can use this option to restrict downloads from certain sensitive websites or web-applications. This will provide users flexibility to download files from all websites except the ones that are unauthorised.