Important Note: This is based on StatCounter, which is definitely not indicative of the overall web. Something like Net Applications gives a much more accurate picture and shows Chrome at 15.51% at Firefox at about 22.57%: http://www.webmasterworld.com/r.cgi?f=145&d=4368971&...
It does vary a lot by geographic region. Europe shows higher Firefox numbers. And, if I recall correctly, Firefox is number one in a few countries (Germany, Russia).
I'm not absolutely sure because Opera, Firefox and all the versions of IE combined have a very close market shares, and yes, Chrome is running up fast too. But I remember Opera held "the most popular single version of browser" the last time I checked.
It does vary a lot by geographic region. Europe shows higher Firefox numbers. And, if I recall correctly, Firefox is number one in a few countries (Germany, Russia).