Adobe have said they'll stop updating and distributing the Flash player at the end of 2020, but fortunately the era of browser games and interactive animations will be preserved. Mike Welsh, who previously worked on the Flash-to-HD video converter Swivel for Newgrounds, is currently working on a program called Ruffle, which will emulate Flash right there in your browser.
Over on the Newgrounds forum an announcement explains, "There is even work being done to create a browser extension that detects old Flash embed code and swaps it with Ruffle, meaning you could visit any old website and the Flash will (eventually) just WORK."
Newgrounds will be adopting Ruffle internally so that Flash projects there will work even without the Ruffle browser extension being installed. "We're adding a true/false attribute to every Flash project to track whether it works in emulation. The initial rollout will cover animated content, then gradually expand to cover more and more games. We'll also be tracking which Flash games are touch screen friendly because they will work on mobile for the first time ever."
This is pretty exciting for the preservation of browser games like The Last Stand 2, Neptune's Pride, or the hundreds of others we played back in the day. You can keep up with progress here.