REDMOND, Wash. (AP)-- Microsoft Corp. is giving its Web browser software its first major upgrade in years, amid signs that Internet Explorer's market share is eroding.

The release late Wednesday brings Microsoft's browser more in line with competing products such as Opera Software ASA's Opera and Mozilla Corp.'s Firefox. Internet Explorer 7, or IE7, adds features such as tabbed browsing, which lets people open several Web pages without cluttering their desktop with multiple open browser windows.

Microsoft has been heavily testing the new browser, releasing five beta versions over 14 months, and has periodically offered security updates for IE6, first released in 2001.

Still, a lag of more than five years between official releases has cost the company. Web analysis company WebSideStory estimates that Internet Explorer's U.S. market share is about 86 percent, while Firefox commands about 11 percent of the market and smaller offerings account for the rest. Two years ago, IE had about a 93 percent share.

Dean Hachamovitch, Microsoft's general manager for Internet Explorer, acknowledged the company could have done more sooner, but he said the new version should address users' concerns. "We did have active development," he said. "The question is whether it was enough."

Matt Rosoff, analyst with independent researchers Directions on Microsoft, said Internet Explorer is important to Microsoft's business because most people believe an operating system should include a way to immediately access the Web.

Still, he said, Microsoft may not have seen much reason to spend a lot of money upgrading sooner since most people continued to use the older version.

Rosoff said the new product includes enough improvements to lure back some users.

But Colin Teubner, an analyst with Forrester Research, said people already using Firefox and rival products might not immediately come back. That's partly because those users have soured on Microsoft, he said, and partly because IE7 doesn't break much new ground.

"A year ago Firefox was head and shoulders above Microsoft's current offering, and I think even with IE7 it's mostly playing catch up," Teubner said.

But he does recommend that IE6 users upgrade, and he believes Microsoft may surpass competitors with future improvements.