A huge milestone has been reached today with the Firefox download counter rolling over to 1 Billion (that is 1 with nine zeros at the end!) To think, a little under a year and half ago (February 22, 2008) Firefox had just reached the 500 Million Downloads milestone. Percy has this interesting factoid:

One notable thing is the first half of the billion took about 3 years and a half, while the second one less than a year and a half, due to Firefox popularity reflected in the global market share increase, currently hovering 30%.

Looking back at an old CyberNet News Article: Firefox Hits 300 million Downloads! When will it hit 1 Trillion? it was estimated then given the current download trend, the 1 Billion mark would be reached on November 3, 2010.

Source: Mozilla Links