I agree that it would be difficult to project the actual number of users based on the total number of downloads.

On the one hand, not every download would get completed and not every completed download would result into an actual installation.

On the other hand, people could also install without downloading, for instance, from CD/DVD etc. Such installations / users would nonetheless add to the actual user base.

One interesting way of estimating the actual userbase would be to analyze the server logs of active websites and extract the percentage of visitors using Firefox (or any other known browser, for that matter).

After reading this post, we made a quick study of the logs of a few sites (which are available to us). The sites are on different topics, catering to different regions of the world, with different visitor demographics and we found the percentage of Firefox users ranging from about 3.5 all the way to 9-ish.

Bsaed on the data that we’ve currently sampled, I’d say about 6 to 7% would be a reasonable estimate. Exterpolating this to about 1 billion Internet users (as currently estimated), it would work out to about 60 to 70 million Firefox users.

Any thoughts, anybody?