Why doesn't Firefox work on Kenken anymore?

Hi. I have downloaded and installed the latest Adobe flashplayer and told "Manage Plug-ins" to allow it to run and to "remember this decision," but https://www.nytimes.com/crosswords/game/kenken still won't load. I just closed the browser and re-opened it, and checked the "Manage PLug-ins" button, and once again it has not saved the instruction to allow Adobe to run on the site. The site still works fine with Safari. This is really annoying. What am I missing? Thanks!