(Shameless self promotion)
We (Leaning Technologies) are working to preserve Flash content using WebAssembly-based virtualization.
We have developed a Wasm virtual machine (CheerpX) that can run the binary Flash player plugin safely in the client sandbox for pixel perfect rendering of any SWF.
If you want to read more:
https://medium.com/leaningtech/running-flash-in-webassembly-...
https://medium.com/leaningtech/preserving-flash-content-with...
Feel free to drop me any question: https://twitter.com/alexpignotti
Got a tutorial or working demo showing how to set up a site that displays legacy flash content in modern browsers?
Ruffle works great in modern browsers and is open source: https://github.com/ruffle-rs/ruffle