I think different people have different concepts of what smooth and buttery feels like. Native apps have taught people to expect a mostly constant fixed 30fps o

I think different people have different concepts of what smooth and buttery feels like. Native apps have taught people to expect a mostly constant fixed 30fps or 60fps. As smooth as you think Slides was, I doubt it achieved this, because the tooling neccessary to monitor repaint regions and framerates, not to mention GPU compositing, wasn't available in 2008. DOM programming is still a minefield. GPU compositing tricks is not only not fully portable between browser rendering engines, they aren't even fully portable across GPUs, as differing GPU restrictions like maximum texture size, texture memory, et al, impose different limitations on the maximize size of composited regions, how many can animate or update at once, etc.