Hello,
> I was thinking that this info could be displayed in
> notify-osd too.
I have actually tried to do it. It's not possible because the gtk status icon's tooltip-query signal doesn't behave as expected.
> Also I was thinking that firefox should use notify-osd to display when a
> download is finished. I know that an addon for firefox exists so why not
> use it by default?
+1 too, but it'll require Mozilla to natively support libnotify for their Linux client. I'm actually surprised it's still not the case...