Microsoft's share of the worldwide internet browser market has dropped 9% since last year, according to a report.
Research by Statcounter found the software giant's Internet Explorer (IE) fell from 58.4% to 49.9% of the worldwide market in September this year, followed by Firefox with 31.5% of global market share.
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Chrome continued to increase market share worldwide, having tripled from 3.7% in September 2009 to 11.54% in September this year, said Statcounter.
"This is certainly a milestone in the internet browser wars. Just two years ago IE dominated the worldwide market with 67%," said Aodhan Cullen, CEO at Statcounter.
Cullen said Microsoft's agreement to provide EU users with a choice of browsers in line with a ruling by European Commission competition authorities may be to blame for the percentage decline.
In the UK, IE market share fell from 60% in 2009 to 54.6% last month, while use of Google's Chrome has risen from 4% to 13% in a year.
Microsoft recently released the beta version of its latest web browser, IE 9, which uses HTML 5.0 and DirectX graphics acceleration.