Microsoft's new Web browser, Internet Explorer 8, is now available in a beta version meant for ordinary users, and it's a pretty good piece of software.

Besides the private browsing mode, called InPrivate, which Microsoft has already announced, there are other nifty features. When your cursor moves over, say, an address on a Web site, one of IE 8's so-called Accelerators drops down a menu bar of different Web mapping services. Click and the address is mapped. No copying and pasting across Web sites.

IE8 has also been designed so that tabbed Web sites are isolated. That means a poorly behaving Web site won't crash the whole browser, just that tab.

The list goes on, and Microsoft explains all the new features on its Web site.

IE 6, introduced in 2001, was a mess, really opening the door for the open-source project Firefox, which is richly supported by Google. IE 7, analysts say, was a major catch-up effort, while IE 8 is Microsoft's bid to move ahead of Firefox and Apple's Safari in performance, features and user experience.

"In things big and small, it is a better experience," contends Dean Hachamovitch, general manager of Microsoft's Internet Explorer group.

We'll see. But Microsoft's new entry and the revived competition in the browser market brings a sense of deja vu. I think back to the comment made by Marc Andreessen, Netscape's co-founder, in the heady days of the browser pioneer's ascent. The browser, he said, could "reduce Windows to a set of poorly debugged device drivers." Translated: the operating system would be relegated to plumbing, while all the action for users and programmers would be on the browser, riding above the operating system.

On the witness stand in 1998 during Microsoft's federal antitrust trial, Jim Barksdale, Netscape's chief executive, tried to dismiss the Andreessen comment as a young man's flippant joke.

But it was no laughing matter to Microsoft, and that potential threat was the animating force behind the tactics Microsoft used to stifle the Netscape challenge.

Today, the browser challenge — though not Netscape — is alive and well. And it is far more realistic now. The tools for making richer Web-based applications have vastly improved. There is the rise of cloud computing, with its promise of shifting all sorts of computing tasks from e-mail to word processing onto the Web. And there is the proliferation of powerful cellphones that can handle many computing tasks via a mobile browser.

So the browser could become "the universal client," noted Peter O'Kelly, an independent analyst. And Andreessen was "just ahead of his time," O'Kelly said.

Firefox is now a credible competitor to IE, with its share of the browser market having climbed to 19 percent, according to Net Applications, a research firm. Microsoft's IE has 73 percent and Apple's Safari has 6 percent.

IE 8 is Microsoft's answer to the renewed browser challenge. "There's competition now and competition does amazing things," says Matt Rosoff, an analyst for Directions on Microsoft, a research firm.