Microsoft's Internet Explorer (IE) has lost nearly a full percentage point in market share during August, the browser's biggest drop in three months, according to a Web metrics firm.

IE's rivals - Mozilla's Firefox, Apple's Safari and Opera Software's Opera - all extended their shares at IE's expense last month.

But all those browsers, Microsoft's included, now face competition from Google, which launched a new browser, dubbed "Chrome," that immediately grabbed 1 percent of the market, according to Net Applications.

According to California company, IE accounted for 72.2 percent of the browsers used in August to access the 40,000-plus sites Net Applications monitors. That was a drop of about 0.9 percentage points from July, and a departure from the month before, when IE maintained its share for just the third time in the past year.

IE's August drop was the second-largest for the year, lower only than May's 1.1-percentage point fall.

"I can't really explain what happened," admitted Vince Vizzaccaro, Net Applications' executive vice president of marketing. "Perhaps there was some relationship with the launch of IE8 Beta 2. If users are looking at IE8, maybe they're looking at other browsers at the same time, trying to decide which one to use."

Meanwhile, Firefox increased its share by about half a percentage point, climbing from 19.2 percent in July to end August at 19.7 percent. Other browsers also boosted their shares: Apple's Safari went from 6.1 percent to 6.4 percent, while Opera's share hit 0.74 percent, up slightly from July's 0.69 percent.

Within IE's and Firefox's totals, however, there were shifts from one version to another.

As Vizzaccaro hinted, Microsoft's share for its IE8 browser - still in beta - leaped by almost 500 percent in just a few days. Before the 27 August launch of IE8 Beta 2, the browser accounted for only 0.04 percent of all browsers connecting to Net Applications-monitored sites. By Tuesday, IE8's share had climbed to 0.22 percent.

The number of users running Firefox 3.0, the latest version of Mozilla's open-source browser, also jumped last month, moving from 5.7 percent in July to 7.7 percent by the end of August.

Mozilla started offering Firefox 2.0 users an update to Firefox 3.0 last week. Not surprisingly, Firefox's month-to-month gain came in increases to Firefox 3.0's portion of the browser's share.

IE7, officially released in October 2006, slid slightly in August, falling from July's 47.1 percent to 46.8 percent. It was only the second time that IE7 lost market share in the last 24 months, according to Net Applications.

The even-older IE6 continued to lose share in August, ending the month at 25.2 percent, off from July's 25.7 percent.

Google Chrome, which debuted Tuesday, accounted for 1.04 percent of all browsers as of Wedneday, said Vizzaccaro.

"But their numbers will be a lot easier to grow quickly," he said, "than, say, Safari or even Firefox did." Vizzaccaro cited Google's name recognition and dominance in the search field as two reasons why it would be able to show rapid uptake for Chrome.