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.