If you read the chapter that Joel recommends, it talks about the design patterns guys that came in and how the anti-duct tape guys had a role to play in that delay.
Mozilla Firefox was forked from the rewritten Mozilla codebase
> Netscape 6.0 is finally going into its first public beta...Well, yes. They did. They did it by making the single worst strategic mistake that any software company can make: They decided to rewrite the code from scratch.
Re-writing a codebase to spawn a totally seperate application is not the same as when you're doing it to re-release an enhanced version of the same application (with a bumped up version number).