What diagram is this?

I've been reading some -really- old slides about mozilla, and came across this diagram:

http://www.mozilla.org/newlayout/doc/gecko-overview_files/Slide0023.gif

but I never seen this sor开发者_JAVA技巧t of diagram before, it does not seem like a UML 2 diagram. Any ideas?

That's a very old fashioned class diagram. The little dots represent an interface.