Microsoft has been tracking the decline of IE6 on a website for the last six months.

Chrome gained most of the share that IE lost, a trend in place since late 2009 when Mozilla Firefox's growth stalled. Firefox lost about one-tenth of a percentage point in September to end the month at 22.5%.

Firefox is in danger of losing its second-place spot to Chrome: If the two browsers keep to their pace over the last year, Chrome will overtake Firefox in June 2012. That's than projections based on data from rival metrics company StatCounter.

Chrome will crack the 20% mark in March 2012 if maintains its current tempo.

Apple's Safari was the only other browser besides Chrome to gain share in September. Using a boost in browsing by Mac machines, Safari exceeded 5% for the first time, said Net Applications.