Whatever happened to Netscape 4.0/5.0 code?

I remember reading that back in the day, Mozilla/4.0 code was open-sourced, and they were working on improvements to it before it was killed. There was a development version with page reflow and a few other things.

Whatever happened to that? Does anyone know? Has it already succumbed to bit-rot, or is there still a copy out there somewhere?

I've become a bit of Web historian last couple of years, and I've always been a huge fan of Netscape. I'd love to get a chance to play around with it.