The closest you can get is the Seamonkey browser, which forked off the old Mozilla Application Suite that Netscape 6/7 was based on. The last version of Netscape 9 was just a rebranded Firefox 2.x.

There are a lot of decades old embedded systems out there. Every so often you hear about a big company still relying on floppy disks and other old tech, including major railways and airplane companies. Having the source code will help with debugging better than having to disassemble or other reverse engineering.