According to numbers released by French Web metrics company XiTi, Firefox accounted for 14.08 percent of browsers used to access a large sample of Web sites that use XiTi measurement software. That's up from 13.31 percent in April and 11.60 percent in March.
XiTi, which says it monitors more than 148,000 Web sites, showed the biggest Firefox share in Finland, where more than 30 percent of Web surfers used Firefox; Germany, with more than 24 percent, and Hungary, with 22 percent.
"The numbers produced by XiTi resemble data from a variety of sources that we've seen," said Chris Hofmann, the director of engineering for Mozilla, the foundation that produces the Web browser. "The only surprise was the market share in Finland. But the high market share in Germany has been an ongoing trend we've seen for several years."
WebSideStory, a domestic Web metrics company,with 22 percent Firefox share last month.
But WebSideStory's data also reflected the slowdown in adoption rates that has dogged Firefox.
Firefox may be encountering several factors that have slowed its once red-hot growth rate.
One is a simple law of numbers--it's easier to grow market share 10 percent per month when starting from a handful of users than it is after your product has enjoyed more than 60 million downloads of its various versions, as Firefox has.
Another is that Mozilla's original pitch for Firefox, that it was more secure than Microsoft's Internet Explorer browser, has suffered from a string of widely publicized.
Mozilla said it wasn't concerned about the market share data and denied a slowdown was under way.
"Looking at all the data sources as a whole is the way we've found value, and we haven't seen a slowdown," Hofmann said. "We still see an upward trend. Some are growing faster than others, and we see these periodic slowdowns. At some point, we are going to slow down, but we haven't seen any kind of sustained numbers to tell us it's here yet."
XiTi, based in Bordeaux-Merignac, France, listed Firefox market share for 24 European countries. At the bottom of the pile were Luxembourg, with 10 percent; Lithuania, with 7 percent; and Monaco, with 6 percent.