Why bother emulating it, though? If you can recognize it, and recognize that it's not using any unusual settings, you could potentially just replace the whole thing with a native video player.
That's a good question. Video is just one use case for Shumway. This specific use case might be better supported by rewriting Flash <object> tags with an HTML5 video player, but Mozilla dislikes adding hacks to workaround site-specific quirks. The hacks are technical debt carried by Firefox on behalf of websites that don't bother to maintain themselves. Mozilla even removes moz- prefixed DOM APIs and CSS attributes when the standardized, unprefixed name is supported.
