I'm not able to find the panel “sequences" where it was previously possible to add new sequence. I found this feature very usefull when I worked on a long animation, with a large number of layers, but now, with the new interface (interface that I mostly appreciate), I can'st find this functionality. If someone can help.
do you mean "scenes" (which is still supported for both html5 and a3)?
Scenes are not supported in HTML5 Canvas documents. Use movieclips instead.