Here a Screenshot and it did still work on my Sierra 10.12.4 BETA (16E163f) I will explain it once again. 1.) Mount the "mac_plugins-2.8.3.dmg" 2.) Don't run the installer, cause its not compatible !...

You see its running on my side. I use two cams without a problem. My MacOS is Version 10.12.2 Beta (16C53a) and Safari Version 10.0.2 (12602.3.12)

Its a bit tricky, but possible :) When you download the "IP Camera Plugin Installer", klick on it with the right mouse to look inside the app. (Sorry, but i use a german MacOS and don't know how...