If you are running a version of Horizon earlier than 7.10 please read this blog regarding Adobe Flash end of life. You will not be able to just stop updating a browser and continue to use Flash.
https://techzone.vmware.com/blog/adobe-flash-player-end-life-and-vmware-horizon
Chris Halstead
Senior Staff Architect, EUC Technical Marketing
chalstead@vmware.com
Twitter: @chrisdhalstead