Firefox 4, which launched last week, has attracted considerable interest among technology enthusiasts. The browser was downloaded 7.1 million times during the first day of availability alone. It passed 15 million downloads within the first 48 hours and is currently nearing 40 million total downloads.

By comparison, Microsoft's recently-launched Internet Explorer 9 only netted 2.5 million downloads during its first 24 hours. Firefox 4 is also outpacing Internet Explorer 9 in actual usage, according to statistics provided by StatCounter and Net Applications. They show that Firefox 4 usage represents between 4 and 5 percent of the total browser market whereas Internet Explorer 9 is hovering between 1 and 2 percent.

It's worth noting that neither browser has been rolled out to regular end users via the standard update channels yet—the statistics are based entirely on voluntary downloads by early adopters. Mozilla's Asa Dotzler attributes the early popularity of Firefox 4 to strong grassroots support from the browser's vocal community of independent advocates.

Firefox's cross-platform footprint and backwards compatibility with Windows XP—which isn't supported by IE9—may also have played a role in boosting Firefox's momentum out of the starting gate.

In the infographic seen above, Mozilla proudly points out that the total number of Firefox downloads in the first 48 hours alone exceeds the current total population of Los Angeles.