[nical]

At some point we will really need be careful when talking about "native performances". FirefoxOS is written in JS on top of Gecko which is as "native" as it can be. if an app's UI is well written, all of the computationally expensive stuff happens in gecko. A good way to see that it is not about being native it is to compare Android and FirefoxOS on the exact same phone. "native performances" still makes sense if you are talking about building physics engines or whatever kind of heavy simulations, but not for 90% percent of the smartphone apps today.

[rimantas]

  > "native performances" still makes sense if you are talking 
  > about building physics engines or whatever kind of heavy
  > simulations, but not for 90% percent of the smartphone
  > apps today.

You have no idea what does it cost to have 60fps scrolling of the non-trival view.

Update: after watching this video: http://www.youtube.com/watch?v=Iu8q-oISbas I do not understand how anyone can call UI responsive and maintain a straight face. Or I do not know what are you comparing it to. Just take a look how the contacts app works :(

[nical]

I do have ideas. I also have a decent knowledge about how Gecko's graphics engine works internally. And again, the expensive operations (actual image rendering, layout computation, compositing, etc.) all happen in the platform, that is in "native" C++ code. What it costs to to have a good scrolling experience is to write your app in a way that doesn't cause the engine to over-invalidate and compute reflows all the time. Or it costs beefier hardware, but then this is not part of the debate of web vs native.