The Shumway Open SWF Runtime Project
theweatherelectric writes "Mozilla is looking for contributors interested in working on Shumway. Mozilla's Jet Villegas writes, 'Shumway is an experimental web-native (Javascript) runtime implementation of the SWF file format. It is developed as a free and open source project sponsored by Mozilla Research. The project has two main goals: 1. Advance the open web platform to securely process rich media formats that were previously only available in closed and proprietary implementations. 2. Offer a runtime processor for SWF and other rich media formats on platforms for which runtime implementations are not available.'"
See also: Gnash and Lightspark.
Which is why a browser-based method is better than a plugin-based method for stuff that Flash does. After all, if you allow Flash for one site, who knows what sorts of Javascript and resources it pulls from other sites?
But a browser based version or HTML5 means site-specific restrictions are honored - a Flash video that wants to pull in javascript from ad trackers can do it via the Flash plugin, but if it was in HTML5 or a browser implementation, will still remain blocked.