What about Chrome, before it added extensions? What about Safari? There are a vast number of ways that other browsers are better than IE, the extensions are just one component of that.
Some of the other browsers definitely have a feature set that's more compelling without extensions. FF really doesn't for me though. The two things I can think of are a slight increase in speed, and the awesomebar (which actually negates some of the speed advantage because it's so slow).