IE10 continues on IE9’s path, directly using what Windows provides and avoiding abstractions, layers, and libraries that slow down your site and your experience
And I think that's quite much the truth. Firefox uses all kinds of libraries between, like the whole XUL thing that makes the interface feel slow compared to other applications that use Windows API directly.
He is also probably talking about native hardware support for HTML5 elements that can be done faster that way. I personally use Opera and they're having hardware rendering coming, but it's still not finished. Firefox doesn't have such at all.
I think the word native is used like it should be - the browser is designed for the OS it runs on and uses it features directly. None of the other browsers do that, because they have to support linux and mac and other OS too.
"We are on the verge: Today our program proved Fermat's next-to-last theorem." -- Epigrams in Programming, ACM SIGPLAN Sept. 1982