Mozilla's Firefox browser lost market share last month, web metrics company Net Applications reported on Wednesday. But Apple's Safari continued to gain ground, an indicator of a slow but sure uptick in Mac sales.

In January, Firefox accounted for 13.7 per cent of the browser usage market, Net Applications said, down slightly from 14 per cent the month before. The dip was the first since May 2006. Since then, Firefox's share has risen continually month to month.

"It appears to be a real dip," not a statistical anomaly, said Vincent Vizzaccaro, Net Applications' executive vice president of marketing and strategic relationships. "It's still bigger than November, though, as if Firefox had a little spike in December.

"Firefox has had minor setbacks like this before," said Vizzaccaro.

More conspicuous than Firefox's slip, however, has been Safari's steady march. The browser, which is based in part on the open-source Konqueror, boosted its share to 4.7 per cent in January from 4.2 per cent in December. A year ago, Safari held 3.1 per cent of the browser market.

"The more interesting trend is on the Safari side," said Vizzaccaro. "It looks like it's taking share away from browsers in the Windows environment."

Net Applications, which also tracks web users' operating systems, said that the increase in Safari's share has been matched move for move by a climb in Mac OS X use. In January, the combined PowerPC- and Intel-based Mac OS X share was 6.2 per cent, up from December's 5.7 per cent. "Both Safari and Mac OS X are heading in the same direction — up," Vizzaccaro said.

Windows XP still maintains its lead in operating systems, however, with 85 per cent. Microsoft's Internet Explorer accounted for 79.8 per cent of the browser market in January.

Windows Vista, which debuted to businesses in November but only hit retail in January, had just 0.2 per cent share by then, according to Net Applications.