Great forum and a lot of great help. Thanks, everyone.
I just set up my Unraid/Plex server and was having problems with this issue. This post gave me what I needed.
In Firefox, when you click on the "Share tab for each of your User Shares," it is just showing a blank page. Once the light went on after reading this post, I was able to make the changes I needed quickly using the Microsoft Edge browser. I don't know if anyone here can fix this, but it would be nice to be able to make these changes in Firefox as well.
One other thing. What is the difference in the unraid security settings between 'pubic, secure and private'? Probably what I actually want to understand here are the nuances of the "Secure" setting.