Not only does it render much faster, it renders prettier, in my opinion.
(MathJax, despite the misleading name, doesn't really do any AJAX. It uses HTML and CSS tricks to produce pretty, well-formatted formulas with a minimum of images. Because it's using real text, it looks better on high-dpi screens, too.)
(defun fibs (n &optional (a 1) (b 1)) (take n (unfold '+ a b)))