[hsivonen]

That screenshot is from Netscape 6—a Gecko-based Netscape release without “Navigator” in the name. The mechanism mostly survives in Gecko today except for the Latin unification (previously split to Western, Central European, etc.).

[ptx]

Oops! It was definitely there in Netscape 4, but I was a bit sloppy with the image search. Here is the Netscape 4 screenshot:

http://www.alanwood.net/unicode/mac_net472.gif