How does a LockDown Browser have the required permissions to perform its functions?

Suppose you have a LockDown Browser such as this: https://www.respondus.com/products/lockdown-browser/

How does the codebase have the permission by the operating system to prevent access to other websites or applications on the computer? You can't do it with JavaScript, for example. I can imagine this could be used in Ransomware.

Thanks.