Well, it is actually Iceweasel 3 for Debian testing. Iceweasel just hit unstable yesterday (it had been for a while on experimental) and if you are running testing and can't wait for it to get through QA, I've made a backport for you:

deb http://debian.axiombox.com/ testing main

The newest xulrunner was also backported, which was, yes, the whole point for this.

UPDATE: Iceweasel 3 was uploaded a couple of weeks now, not yesterday