This seems to be a problem that won’t go away. It seems inordinately hard to get a good looking set of fonts of the correct size. It is not that there aren’t some nice fonts available; there are, at last, some fonts under Linux that often look superior to the Microsoft ones. It’s just that it is difficult to get the whole look and feel correct. This is especially true when mixing Gnome based applications (Firefox and Thunderbird for example) and KDE.