Microsoft has kicked off a new marketing campaign for Internet Explorer 9 (IE9) that urges users of rival browsers to run it, even if only sparingly for "a few sites that you go to everyday."

The unusual approach, which Microsoft launched last week on, a domain it registered last month, is part of Microsoft's continued campaign to convince Windows users to stick with IE9, or if they've switched browsers, to give it another try.

"One of the more interesting trends these days is the number of Chrome and Firefox enthusiasts who have 'added' Internet Explorer 9 into their browsing mix," said Roger Capriotti, the director of IE marketing, in a blog post last week. "You don't need to ditch your current browser, but there are probably a few sites you go to each day like Facebook that you can pin with IE9."

"Pin" refers to IE9's ability to place websites on the Windows 7 taskbar for one-click access. The feature has been heavily promoted by Microsoft.

In the blog post, Capriotti repeatedly argued that even users who had defected to Google's Chrome or Mozilla's Firefox should run IE9, if only occasionally.

"It's the perfect complement to whatever browser you use for daily tasks," he said.

Capriotti also couched IE9 as a "comeback" for Internet Explorer, and said that the browser has been in "many ways ... a turning point" for Microsoft.

Browser usage share data doesn't support his argument. In the year since IE9's launch, the total usage share of IE has fallen 5.5 percentage points, a loss that represents about 9.4% of IE's March 2011 share. During that same period, Chrome grew by 56.5%, adding 6.8 percentage points.

Almost since IE9's debut, Microsoft has ignored IE's continued decline and has instead focused on the growth of its newest browser on Windows 7, a combination the company has regularly claimed is the only metric that matters.

In February, IE9 accounted for 30.1% of all browsers running on Windows 7, Capriotti said last month, citing statistics from Web measurement company Net Applications, making it the most popular single edition on the operating system.

IE9's global usage share on all operating systems is considerably less: just 12.6%, or less than half that of the older IE8.

Even with its shrinking share, IE remains the world's most popular browser: All versions of IE accounted for 52.8% of the browsers run during February, while Firefox and Chrome claimed 20.9% and 18.9%, respectively.

In another blog post, Capriotti made Microsoft's clearest defense yet for the numbers published by Net Applications, casting them in contrast to those from Irish metrics company StatCounter.

Net Applications, Capriotti noted Sunday, has long weighted its results by country -- using the estimates provided by the Central Intelligence Agency (CIA) for each nation's pool of online users -- and recently revised its data to account for Chrome's "pre-rendering," a trick that eliminates the sites that the browser downloads but may never show the user.

Both make Net Applications' figures a more accurate estimate of browser share, Capriotti said. In comparison, because StatCounter does not weight its data by online populations, it over-reports the shares of both Firefox and Chrome, and under-reports IE's.

StatCounter regularly shows IE with a smaller usage share than Net Applications: In February, for example, StatCounter had IE's total share at 35.8%, or about 17 percentage points lower than Net Applications.

As Microsoft has pointed out, IE9's share is tightly tied to Windows 7, in large part because the company decided not to support the decade-old Windows XP, which powered 49.4% of the PCs that went online last month. In that same period, Windows 7 ran 41.5% of all Windows PCs.

Microsoft's focus on newer operating systems will continue with IE10, which will run only on Windows 7 and the upcoming Windows 8. IE10 will not support the slowly declining Vista.

There is a bright spot for IE overall all, however.

In the past 90 days, IE's share has grown slightly, increasing by two-tenths of a percentage point. Chrome's share, meanwhile, dropped by about the same amount over the last two months.