Firefox ESR does not allow Silverlight anymore. Unable to launch SilverLight.
On Mac computers the best browser we have found is Seamonkey version 2.49.4. You can download Seamonkey in the below Link
The only caveat is when launching the browser for the first time, hold control and click the app to successfully launch it the first time.
The Catalina OS blocks Silverlight. At this time, the only way to use ThunderCloud on a Mac running Catalina is to run Windows using Bootcamp, Parallels, or other virtual software. Once Windows 10 is installed, you can install the XOS ThunderCloud app from the Microsoft Store