So let’s talk about Ruffle. This is one of the latest attempts to rebuild Flash. And by that I mean, this is a Rust-based emulator of Flash. Mozilla tried their hand at it before with Shumway but well, that died. This is another go at it.
It’s still not quite at “drop-in replacement” stage yet and its ActionScript support isn’t all there yet, but hey, there’s a demo page where you can play an old take on Metal Slug if you want!