Nope running the stable branch... on vista. (yes it is stable on XP).
I'm liking Iron 5. Getting used to the differences. Mainly no bluescreens of death - ultimately attributable to Flash, but it is the browser's design that determines how far it goes. Once Noscript 2 borked my firefox install I said to heck with it. Firefox is nearing the end of its lifecycle in my view.
Note that a new "feature" of noscript assumes you are a router idiot and constantly connects to the developers website comparing your internal and external IP addresses constantly. Bad move. Borking my firefox? Worse. An extension should not be able to cripple the browser. That is Mozilla's fault, not the Noscript people, though I've had enough of both.
My advice is to drop noscript if you stick with Firefox. Don't they have a new browser project on the go? Seamonky? (more Netscapey?) Nah, to heck the that, the old netscape code should finally go.
I like the Chromium-based Iron. I also like Safari, but I reject it on the principle that it is an Apple product (even though it is a good one).
I'm kinda sad to say goodbye to Firefox but I think it is time. Once a browser reaches a certain level of popularity, I do not want to use it anymore. Hopefully something else will come along once Chrome overtakes Firefox or perhaps the paradigm will change entirely. Which the mobile market will probably do ultimately.