Oh I thought you where trying to prevent an application from starting an other application (which has to be controlled by Defense+).
If you try to block an application from accessing the Internet via Browser X that won't work on Firewall rules.
What happens is the following, KMPlayer call's default browser, default browser X starts and then tries to access the Internet.
So you would have to create a rule specific for Browser X so it's can't access 'domain X' or IP Y etc, that's probably to complicated.
It's much easier to prevent KMPlayer from opening the browser in the first place.