Why would they optimize the code for a prototype? It would make very little sense, especially since they have their own browser. I'm fairly certain this is the exact same tarball that my link has. That would be the GPL, but since the binary was not released (this does not count as a release), they are not obliged to release it. But if n950 just uploads the firefox binary you can do a diff with the tarball from my link (armeabi version), and you'll most likely see it's the same.