Pale Moon forked off early enough from Firefox to not be affected by that move (a lot of other "forks" like Cyberfox, SeaMonkey, etc waited too long to actually fork off into their own codebase and got seriously screwed over). And yes, the devs have publicly stated that they intend to keep supporting plugins like Unity until the bitter end. So technically, there is still at least one browser that officially supports this game, lol.