Mozilla's open-source Firefox browser has gained 30 million users over the past eight weeks, as it continues to gain on Internet Explorer.
Chief executive John Lilly revealed the increase in user adoption in a Twitter post on Monday, and Tristan Nitot, president of Mozilla Europe, confirmed it to ZDNet UK on Tuesday.
"We've seen a significant increase in the number of users for Firefox," said Nitot. "Firefox checks for new versions every 24 hours, when it's running, and when it checks, it pings the Mozilla server. We count the number of pings."
Nitot explained that counting the requests gives Mozilla the number of active daily users. To calculate the number of monthly users, the organisation multiplies the number of active daily users by three, to adjust for days when people are not browsing.
Over the past eight weeks, Mozilla has seen an average increase of 10 million daily users, from approximately 103 million to 113 million. That translates to a total of approximately 330 million monthly users .
"It's amazing to have 330 million users," said Nitot. "That's the size of the population of the USA."
In terms of global rankings, Firefox has steadily gained market share since its launch, while the dominant browser, Internet Explorer, has gradually lost user numbers.
According to US-based web-analytics company Net Applications, Internet Explorer held 65 percent of browser market share worldwide at the end of September this year, a drop from 70 percent in November 2008. By contrast, Firefox gained almost three percent, rising from 21.21 percent share to 23.75 percent.
Firefox usually sees a seasonal jump in user numbers in the autumn, according to Nitot, who added that people going back to work after northern hemisphere summer breaks could be contributing to the tally.
"Usually it's a mixture of back-to-school, and people getting new computers and installing the latest version," said Nitot. "This boosts our numbers every year."
In 17 countries in Europe, Firefox is now the dominant browser, he said, and the browser is particularly popular in Eastern Europe. Polish web-analytics company Gemius Ramking puts Firefox consistently at the top of its browser rankings chart for the region. For example, Firefox has over 48 percent of market share in Poland.
In addition, the mass adoption of information technology over the past four years in Eastern Europe has helped uptake of Firefox, Nitot said. "Internet adoption came while Firefox was becoming popular," said Nitot. "In Eastern Europe, they were not used to Internet Explorer 6. There was not the muscle memory of clicking on the blue E."
However, Nitot added that Firefox was also popular in Western Europe, particularly in Germany, as people there place an emphasis on privacy. In Europe in general, the ethos and enthusiasm of the local Firefox development communities tends to encourage new users, he said.