Mozilla has reached an impressive milestone for the Firefox browser, which has now totaled over 400 million downloads since its inception. While this of course doesn't tell you at all how many people are using the increasingly popular browser, for something almost unheard of just a few years ago it is quite an achievement.
Given that if you use Firefox, you've likely downloaded it many times yourself, no one is going to use this figure for statistics. It does demonstrate demand, however, and month after month we have seen Firefox usage spread. IE7 has helped Microsoft bring some of that back - but not by a lot. Depending on the region you are in, Firefox has anywhere from 10% to 40% of the browser market. In comparison, in 2004 Firefox struggled under 3%.
I do hope they can continue to gain market share - I hope, however, that it doesn't come at the cost of browser quality.