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I've downloaded FireFox probably twice on my Windows box, once on my iBook and a couple of times in FreeBSD.
I personally think that the count of the same people downloading FireFox multiple times on the same machine, and the figure of how many times one person has downloaded it on more than one computer cancels each other out.
Non-savvy users nornally aren't known to download an application many times (if at all). Mostly computer enthusiasts will be downloading it many times, and guess who has more than one computer entirely to himself? That's right, Mr. Geek does.