We are all thankful now that IE is on its last iteration. Spartan, from I have seen, renders a lot like FireFox.
However, most of the corporate environments I have seen still use IE, and are 2 to 4 versions behind the consumer market.
This pattern only applies to desktop. On the mobile front, I am seeing a neck to neck between Chrome, FireFox, and Safari. Because of that, I also prioritize FireFox then Chrome on mobile fronts.
In short, there no news here, but more of a status and reminder to look at your consumers before deciding what is your primary development target.
Brian By Experience 