Firefox PR reached the number of 1 million downloads (that’s one-zero-zero-zero-zero-zero-zero) in about 4 days, 6 days earlier than aimed for.
And it’s just a Preview Release!
My guess is that the number of downloads after day 10 will be something about 2 million.  You can follow the march to 1 million downloads (and further) in the Spread Firefox Campaign website.