Sorry for this silly question:
I really don`t know what a layer is (maybe because I never used Netscape ?). Would anyone be so kind and expain what it is, how it works and what it is good for. Thanks.

It's just another browser window, but *displayed* within the *same* window, with the various open layers shown in a toolbar in the browser instead of many windows in the taskbar. As for it's relative merits, i suppose somebody else will have to answer that... like any user interface element, it's largely a matter of taste, i would say.

Now I understand ! Thanks a lot.
Indeed: I can`t recognize it`s merits, too.