But IE hasn’t had a significant overhaul in five long years. That has allowed competitors like Mozilla’s Firefox and Apple’s Safari to leap ahead in terms of features. In fact, many of the savviest Web users have abandoned IE in recent years, partly because of the growing feature gap and partly because of IE’s persistent security problems.

Now, finally, the software giant has produced a major new version of the browser, called IE 7. It’s a fundamental rewrite, especially in the areas of user interface and underlying security.

But competitors haven’t been standing still. Mozilla is almost done with its Firefox 2.0, a more minor update of its browser than Microsoft’s undertaking.

I have been testing IE 7, and I agree with Microsoft that it’s much improved. If you are a confirmed IE user, upgrading to this new version makes perfect sense, because it is likely to be more secure and its new features make Web browsing better. But if you are already using Firefox, IE’s main competitor, I see nothing in IE 7 that should make you switch. It’s mostly a catch-up release, adding to IE some features long present in Firefox and other browsers. The one big feature in IE 7 that wasn’t already in Firefox, a built-in detector that warns against fraudulent Web sites, is being added to Firefox in version 2.0.

The new Internet Explorer, which is free, runs only on the latest revision of Windows XP and the forthcoming Windows Vista operating system, while Firefox offers nearly identical versions for Windows, Macintosh and Linux computers. IE 7 will be offered automatically to Windows XP users — gradually over the next few months — via the Windows update program. Microsoft will also make it available for manual download.

The biggest change in the new IE is tabbed browsing, the ability to open multiple Web pages in a single window, and to switch among them by clicking on tabs at the top of each page. This allows you to quickly scan a whole bunch of Web sites at once. It’s especially useful if you group bookmarks (which Microsoft calls Favorites) into a folder, and then open all the pages in the folder at the same time.

In my view, tabbed browsing is the best improvement to Web browsers in years, and it has long been built into Firefox, Safari and other browsers. Microsoft’s implementation is OK, but is curiously inconsistent. You can open all of the sites in any folder in your Favorites list in tabs, with a single click. But this works only if you are viewing your Favorites in a side panel at the left of the screen. If you have a folder of Favorites in the Links toolbar at the top of the screen, as many power users do, there’s no way to open all of the pages it contains with one click, as you can do in Firefox.

The other big change in IE 7 is that there is now a search box built into the user interface itself, which allows you to perform searches without first navigating to the home page of the search service. You can choose which search engines this feature uses. Again, this feature is old news for Firefox and Safari users, but it should eliminate the need for add-on toolbars, like those offered by Google and Yahoo.

The overall interface of IE has also been cleaned up and simplified. The menus are now hidden, and the little animated flag in the upper right-hand corner is gone. You can make the menus appear if you like, and you will need to do so to get to some features, such as the screen that lets you organize your Favorites.

The only really notable new interface feature in IE 7 is something called Quick Tabs, which lets you view, on one page, thumbnails of all the pages you have open in tabs. You can quickly switch among them, or close any of them, from this view. It’s very nice, but reminiscent of an Apple feature called Exposé.

On the security and privacy front, Microsoft says it has made many changes under the hood to harden IE against hackers and the authors of malicious software. The browser now warns you when you are at a Web site that may be a fake (called a phishing site) and moves you off that page unless you insist on going back to it. There is also a much easier way to clear out all traces of your Web activity, another catch-up feature.

But the most important new security feature in IE 7 — something called Protected Mode, which stops Web sites from changing your computer’s important files or settings — will work only in the new Vista version of Windows, due next year, not in Windows XP.

Ironically, the improved security in the new version may erode IE’s greatest strength: its broad compatibility with Web sites. Some sites may not work properly in IE 7 because techniques they used are blocked by the new security features.

In addition to matching IE 7′s antiphishing warning feature, Firefox 2.0 will feature a spell checker, a system for suggesting popular search terms, and a way to resume where you left off after a crash, among other things.

The new Internet Explorer is a solid upgrade, but it’s disappointing that after five years, the best Microsoft could do was to mostly catch up to smaller competitors.

Email me at mossberg@wsj.com.