I'm not sure if this is the corrent list to discuss things related to 
binary packages on ftp server, but...

ftp://ftp.netbsd.org/pub/NetBSD/packages/pkgsrc/www/firefox/README.html
The webpage lists firefox-1.0nb1 for sparc64 platform (I haven't tried 
others), looking at the requirements list above, it shows the package 
depends on gtk2 and its friends. So I get the package run pkg_add and I get:

# pkg_add firefox
pkg_add: Warning: package `//./firefox-1.0nb1.tgz' was built for a 
different version of the OS:
pkg_add: NetBSD/sparc64 2.0 (pkg) vs. NetBSD/sparc64 2.99.16 (this host)
pkg_add: no pkg found for 'ORBit-0.5.15nb6', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `ORBit-0.5.15nb6' failed!
pkg_add: no pkg found for 'ORBit>=0.5.15nb5', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `ORBit>=0.5.15nb5' failed!
pkg_add: no pkg found for 'gdk-pixbuf-0.22.0nb2', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `gdk-pixbuf-0.22.0nb2' failed!
pkg_add: no pkg found for 'gdk-pixbuf>=0.22.0nb2', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `gdk-pixbuf>=0.22.0nb2' failed!
pkg_add: no pkg found for 'gtk+-1.2.10nb7', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `gtk+-1.2.10nb7' failed!
pkg_add: no pkg found for 'gtk+>=1.2.10', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `gtk+>=1.2.10' failed!
pkg_add: no pkg found for 'gtk+-1.2.10nb7', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `gtk+-1.2.10nb7' failed!
pkg_add: no pkg found for 'gtk+>=1.2.10nb6', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `gtk+>=1.2.10nb6' failed!
pkg_add: 1 package addition failed

Looks like the binary package should be under www/firefox-gtk1