Web site measurement and marketing company WebSideStory on Tuesday said that as of April 29, IE fell a percentage point in domestic share to make up 88.9 percent of browser usage, while the Mozilla Foundation's open-source Firefox browser rose just over a point to 6.8 percent.
The single-point gain represents afor Firefox. While the browser gained a half point of market share per month in the period after its test launch in June, and a whole point per month in the period after its 1.0 launch in November, it's now gaining just over one-third of a point per month.
"The pace has slowed down again," said WebSideStory analyst Geoff Johnston. "We started to notice that trend in the last release."
The slackening of Firefox's growth could mean that the browser has converted a substantial proportion of its natural constituency, thought to be early adopters and the technically savvy. It could also show that the browser's widely publicizedhave begun to that people should switch from IE to be safer.
The Mozilla Foundation warned against assigning too much importance to falling growth rates, and said the Firefox security profile still bested the competition's.
"We've had a few security updates, but they've been for potential vulnerabilities, for staying ahead of the curve of potential problems that might come down the road for Firefox users," said Chris Hofmann, Mozilla's director of engineering. "You don't have widespread reports that people are being exploited when they use Firefox. I'm not sure there's any evidence that people are migrating away from Firefox because they feel less secure."
On the contrary, Hofmann said, Mozilla has earned kudos from security-minded users for quickly turning around patches before holes are used for actual exploits.
Whatever its cause, the growth slowdown calls into question the viability of one of Mozilla's stated goals for the year:.
Johnston said that Firefox could not allow its growth rate to fall any further if it expected to achieve that goal.
"It's going to take no erosion and maybe a little bit of an uptick to surpass that by the end of the year," said Johnston, hedging a WebSideStory release that said Firefox was "well on its way" to achieving 10 percent this year. "It's going to be a bit of a close call. It may depend on what they come up with in a new version this summer."
Hofmann called the 10 percent goal "aggressive" and said the foundation was doing what it could in terms of distribution deals and marketing campaigns.
Even before its formal launch in November, Firefox began to revitalize a market long ceded to Microsoft, capitalizing on security concerns about IE and dissatisfaction with features to force Microsoft below the 90 percent mark for the first time in years.
Many credit Firefox's success with goading Microsoft intoafter years without a significant upgrade.
Firefox late last monthof its browser since the Version 1.0 release in November. Downloads do not equal users, because a single user often downloads multiple copies for different computers or to replace the browser with patched versions, of which Firefox has had three.
Along with its numbers for the United States, WebSideStory also released data for Germany and Japan, which illustrate the international extremes of Firefox penetration.
In Germany, IE accounts for 69.5 percent of browser usage, while Firefox makes up a whopping 22.6 percent. In Japan, by contrast, IE commands 93.9 percent of the market, and Firefox a mere 2.8 percent.
Even as its numbers painted a troubling picture for Firefox's growth, WebSideStory called attention to the browser's overall success in making gains against the IE juggernaut.
The slowdown "can be looked at in a couple of ways," Johnston said. "One is that Firefox adoption is starting to slow, and another is that it continues to plug ahead. Last June, I would never have thought that Firefox would keep growing for a full year, because Microsoft had never moved backwards."