As a work around, you can still get your hands on old versions of Firefox that will support old versions of the Java plugin.
I would suggest using an Extended Support Release rather than experimenting with older, possibly buggy, possibly insecure versions. The Mozilla Firefox 52 32-bit ESR / Extended Support Release as of today April 20, 2017 continues to support NPAPI based plugins (i.e. Java). You can download that version here: https://www.mozilla.org/en-US/firefox/organizations/
Remove any version of Firefox you have and install this version.
The Exception Site List feature of the Java plugin was introduced in Java 7 Update 51. You'll need that feature to get the Media Master to work but you need to stay away from updated Java plugins.
You can download the Windows x86 Offline Java installer for Java 7 Update 51 here: http://download.oracle.com/otn/java/jdk/7u51-b13/jre-7u51-windows-i586.exe (you'll need to create an account). If you don't trust me to access the EXE directly, the official Java archive page is here: http://www.oracle.com/technetwork/java/archive-139210.html You can start there and find it yourself.
- - Un-install all your other versions of Java and install this one.
- - Go to Control Panel | Java 32-bit | Security and set your security level to medium.
- - Go to Control Panel | Java 32-bit | Security | Exception Site List and add you Unity Connection Publisher and Subscriber. Use the format https://
You should now be able to run the Unity Connection Media Master (at least back to version 8.6) in Firefox, play, upload and save greetings. You may still be prompted a handful of times to allow Java to run, and possibly have to save the greeting multiple times in Unity Connection after SSL pop-ups, but it works.
Trust me. I did it yesterday.
Don't forget to delete this version of Java and Firefox before your IT security team freaks out.