usually, that desktop icon is more than merely an icon - it's a launcher of some sort (in reality it is just a file) which you'd need to edit (with a text editor, or right-click -> properties) so that it launches your choice of application. The launcher will have some sort of "target" attribute, or "path to application" attribute, which you would set to be the path to your new Firefox.
Or, do you have any kind of right-click context menu, if you right click the desktop, whereby you can create a NEW launcher icon?
Also, there's a section at the very bottom of the page you linked, called:
“How do I get a Firefox 3 icon in the Quick Launch taskbar, like/instead of Firefox 2?”
Have you tried what's suggested there? Or is that instruction specific
to the menu
button, rather than the desktop
I don't use Xandros, and I do not believe a whole whack of other LQ members do either, so we do not get frequent questions about that OS; please be patient with us
and hopefully we can work together to get your icons sorted out.