I suspect that the error here is between patent and copyright. You
can't patent Mosaic. You can patent the idea of a WWW browser in theory,
but I bet you can't in practise.
Spyglass, as far as I know, does hold the Mosaic copyright or some
rights. Copyright over Mosaic has no effect on Netscape, which was entirely
rewritten - ie has no Mosaic code in it.
Cheers
David Cake