Funny to see this mentioned. Just this morning I was struggling to get ffmpeg-wasm working on Firefox. It should theoretically be possible with HTTPS and configured headers:

  Cross-Origin-Opener-Policy: same-origin
  Cross-Origin-Embedder-Policy: require-corp

Related links:

Does not work in Firefox 79+ because SharedArrayBuffer is undefined - https://github.com/ffmpegwasm/ffmpeg.wasm/issues/106

SharedArrayBuffer: Planned changes to shared memory - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...