Minor point, but I don't like the citation of Netscape as a failed rewrite.
It's worth remembering that the Mozilla project ended up being a success in that it dealt the blow that finally dislodged IE from dominance. The original Netscape codebase could not do this because at the time IE4 was already way ahead in terms of CSS support and Netscape was hitting an architectural dead-end. Maybe they could have piled on some more hacks to get NS5 out quicker, but even if it had feature parity to IE5 they had to contend with Microsoft's bundling which was Netscape's real undoing.
It's worth remembering that the Mozilla project ended up being a success in that it dealt the blow that finally dislodged IE from dominance. The original Netscape codebase could not do this because at the time IE4 was already way ahead in terms of CSS support and Netscape was hitting an architectural dead-end. Maybe they could have piled on some more hacks to get NS5 out quicker, but even if it had feature parity to IE5 they had to contend with Microsoft's bundling which was Netscape's real undoing.