In Firefox, you now need to set up Flash manually (and put it where Firefox can see it) to be able to enable it on sites:https://support.mozilla.org/en-US/kb/install-flash-plugin-view-videos-animations-games
You might have to do that and enable it for Warzone to be able to use the Flash client again. PM me if you need help with this (some of the instructions are _slightly_ out of date); I just verified that Firefox+Flash works for me.In the long run
Like everyone else pointed out, Flash end-of-life is at the end of this year. After that, Adobe will stop maintaining Flash and no browsers will care the least about Flash support. Things might just suddenly stop working one day and unless you're really invested and willing to put in effort to patch all sorts of opaque bugs you will not be able to do a single thing. Give UJS another try. It's considerably better than the old Unity interface and pretty easy to pick up.
Edited 9/3/2020 22:25:33