Here’s how to install the last version of Netscape Navigator (9.0.0.6) on Ubuntu 16.04.
Why would you want to do this? I can’t think of any practical reason.

First you need to download a copy. You can probably find it in multiple places, but I found it at Softpedia.

Next extract it to /usr/local…

sudo tar xvvzf netscape-navigator-9.0.0.6.tar.gz -C /usr/local

…or if you’re a heretic you could use a root file manager (like I did). Now link the executable…

sudo ln -s /usr/local/navigator/navigator /usr/local/bin/navigator

Link Firefox plugins… (this outdated? instruction seems dubious, but didn’t cause me any obvious problems)

ln -s /usr/lib/mozilla/plugins/* /usr/local/navigator/plugins/

And finally, deal with the missing (32-bit) dependencies…

sudo apt install libgtk2.0-0:i386 libpangoxft-1.0-0:i386 libpangox-1.0-0:i386 libstdc++5:i386

You should now be able to run it from a terminal by typing navigator. If you want a launcher, you’ll need to create a .desktop file (in /usr/share/applications/usr/local/share/applications or ~/.local/share/applications) like this…

[Desktop Entry]
Name=Netscape Navigator
Comment=Netscape Navigator Web Browser
Exec=navigator
Icon=/usr/local/navigator/icons/mozicon50.xpm
Terminal=false
Type=Application
Categories=GNOME;GTK;Network;WebBrowser;

If you’d like a higher quality icon here’s the version above in SVG format (source: Wikimedia Commons) to use instead of mozicon50.xpm.