Are these users also able to access the Internet ? If so it maybe better to allow the users to have an up to date and secure version of Firefox, probably the ESR version, and then an additional locked version if necessary for use with your webrtc system. Does that sound like a way forward ? Presumbly you own and control these Company computers. Out of curiosity, what is *The incompatible software? *The Firefox feature that causes you a problem? * The version that you will use for webrtc?