I use Firefox as a default browser. It's current at version 57 and running flash version 26.0.0.151. Play now shows just fine.
I use it for forums and other browsing. It still asks right after updating for you to allow flash, and remember that setting. But it has been doing that for quite a few versions.
Look up in the address bar, if there is a red manage pop up icon,(on the left before the www.) you haven't allowed Firefox to run flash.