The recent market share growth enjoyed by the open source Firefox browser has begun to slow in recent months, according to the latest data from US industry watchers.

Analyst WebSideStory reported today that Firefox's market share gains against rival Internet Explorer slowed to a comparatively modest 15 per cent increase in the five weeks leading up to 18 February 2005.

In the six weeks before that, the web watching firm reported that Firefox grew at 22 per cent. These figures compare with a 34 per cent increase between 5 November and 3 December, which coincided with the release of Firefox 1.0 on 9 November.

WebSideStory chief executive Jeff Lunsford noted that, according to a recent report by the Mozilla Foundation, there have been 25 million downloads of the Firefox browser in the past 100 days.

"The download numbers continue to impress us and the mainstream press. We track usage rather than downloads, however, and are seeing that the growth in Firefox usage has slowed since its big surge in November. This is probably to be expected as we move beyond the early adopter segment," he said.

Lunsford added that at the end of 2004 it seemed that Firefox would achieve a 10 per cent overall browser market share by mid-2005, ahead of the reported year-end goal of the Mozilla Foundation.

"Given the latest growth rates, the year-end target still appears attainable, but a mid-year achievement is unlikely unless we see increased marketing activity from the Mozilla Foundation," he said.