Just to be clear, 500M downloads doesn't mean 500M users. Some users download more than once. Some users deploy multiple installs from a single download. And, many people who download don't become regular users.
Nevertheless, it is an impressive milestone. What does it say about our market share or actual user base? Not much. What does it say about our community? A lot. Over 80% of Firefox users were referred to Firefox by a friend, family member, or colleague. With a marketing budget that's a fraction of a percent of that of companies Mozilla competes with, we've managed to get more downloads of Firefox than any other piece of consumer software I'm aware of.
So, what are our user numbers actually and what is our market share? I estimate that with about 50 million active daily users, that our total user base is approximately 150 million people*. As far as market share, there are a lot of people out there measuring it and they all have different numbers. At the low end, we see Firefox usage at about 17%. At the high end, we see as much as 37%. In between those, there are a range of measures, all with their own biases.
Looking at all of this data, actually, kind of squinting at it with my head cocked at just the right angle, it seems to suggest that Firefox is at about 20% market share worldwide.
So, 500M downloads, 150M users, and 20% market share. Not a bad showing for the four year old Firefox.
* we've added nearly 10M daily active users since John's post in November.
