A significant amount of work is going into both those builds but a lot more is needed. As much as I love having a multiprocess browser the V8 JS engine is the real heart of gold of chrome, and that is cross platform. Just nothing uses it besides chrome as far as I know. I do know that the next Mozilla JS engine feels to me at least (and if you benchmark different apps) just as fast. So the next firefox will be on par with speed and it will be cross platform. It will just have tabs that are not as cool.