Ok, found the problem: the volume from the flash player (btw, skype too) is managed from the "PCM" key in the Kmix. Be sure to enable it (settings> configure channels.
So, I think the downloading of the "Adobe Flash Player plugin installer" from the Kpackage Manager did the work. It was just an issue of volume setting. One can check the plugin by writing about
lugins in the URL bar in Chrome/firefox. There appears if it's installed or not.
Tkx to all!