On multiplying daily usage by 3
@Woodgar @Bernie 2, @ Loki 1
I work at Mozilla, and I would defend the multiplier of 3 * average daily usage as a reasonable estimate for actual usage (although obviously, it is a simplification).
In Europe (including Russia), there are an estimated 402 million internet users, and we see about 47 million daily users of Firefox.
Net Applications reports Firefox market share in Europe at 34.2%, which would mean approximately 137 million European users (assuming 1% users = 1% market share).
This would mean actual Firefox usage is 2.9 times the average daily usage of Firefox.
It does seem likely that Firefox users tend to be heavier-than-average Internet users, but many use more than one browser, (for example they might be obliged to use IE at work). I don't know of any good studies that can account for that, so, all things being equal, a multiplier of 3 seems a reasonable approximation.
Mine's the navy anorak.