You also won't be able to manually install Flash in Firefox 85, and nor should you want to. There are now many open standards like HTML5 and WebAssebly that provide the same capabilities and functionalities that plugins such as Flash first pioneered. Whilst many of us may have fond memories of the software, we shouldn't be trying to hold onto obsolete software for the sake of nostalgia.
Flash has been slowly crawling towards its demise since Adobe made an announcement back in 2017 that it would end support for Flash Player on December 31 2020, with major web browsers such as Microsoft Edge and Google Chrome confirming that the program will be removed to improve security and performance. It's hardly a secret that Mozilla has been looking to remove Adobe Flash from its browser for some time now.