"The uptake curve got steeper between 5 and 6, which means more people are updating faster."
You have to wonder how much of that is a selection effect. Since there was a change in the upgrade tempo in firefox, you'd expect to see the uptake curve get steeper even if overall user behavior hasn't changed, because the users that were on 5 when 6 came out would tend to be the more adventurous ones.
Edit: in other words, ff 5 didn't have as much time to accumulate less-adventurous users as ff 4 did, so the 5->6 transition will appear faster than the 4->5 transition.
You have to wonder how much of that is a selection effect. Since there was a change in the upgrade tempo in firefox, you'd expect to see the uptake curve get steeper even if overall user behavior hasn't changed, because the users that were on 5 when 6 came out would tend to be the more adventurous ones.
Edit: in other words, ff 5 didn't have as much time to accumulate less-adventurous users as ff 4 did, so the 5->6 transition will appear faster than the 4->5 transition.