Hi Hieper. Only the Internet Explorer part of the solution depends on iframes; Firefox uses a timer and checks the location bar at regular intervals.
In time, I hope that browsers bake the kind of functionality in the Really Simple History library right into the browser itself, for improved reliability.
In terms of XHTML, I believe that XHTML is a dead end; see my blog post "XHTML Considered Harmful" at http://codinginparadise.org/weblog/2005/08/xhtml-considered-harmful.html for details.
Thanks for reading and commenting on the article.