I would like to suggest considering adding Ruffle to Firefox as a pre-installed extension, similar to how Flash used to be pre-installed in Chrome
Downsides/potential issues:
1. Ruffle is alpha software
2. Ruffle could encounter issues similar to https://github.com/ruffle-rs/ruffle/issues/4030.
3. I would suggest disabling Actionscript 3 content (the Ruffle extension currently gives a warning for Actionscript 3 content)
4. I would suggest showing a warning, before loading other Flash content, that it may not load accurately, because Ruffle doesn't currently support every feature that Flash had. I would suggest also adding an epilepsy warning, because I once saw an Actionscript 3 game flicker through a few animations really fast on loop, due to Ruffle not supporting Actionscript 3, and I'm not sure if it's possible for that to occur on other Flash content
Benefits:
1. some Flash support is better than no Flash support
2. it would give Firefox something that Chrome doesn't have (at least not without installing an extension)
3. it would boost Ruffle's popularity, which would hopefully result in Ruffle coming out of alpha faster
Thanks for reading