Replying to @mmocny's answer:
NPAPI is also being phased out for extensions.
And considering that NPAPI-using extenions will be rejected in the Webstore AND deployment options for Windows outside Webstore were severely shrunk, it's a bad idea. You may be able to make it work, but it will be temporary and painful.
The correct way to do it now is using Native Hosts. Basically, you have a specifically crafted native executable wrapping Zigfu functionality you need that talks to your app via Native Messaging.
Deployment downside is that you have to install the native component separately, but in your case that's a plus (restricts access) and not a problem (you control the machines).