Version 7 of Microsoft's dominant Web browser packs in interface changes, many new features, and plenty of under-the-hood updates. It also arrives just before version 2 of the up-and-coming Firefox browser, which may be just days away. So which new browser is your best bet?

Firefox 2 offers no radical changes compared with version 1.5, which came out a year ago. It's a measured step, purposely non-jarring for current Firefox users. A built-in antiphishing tool makes its first appearance, but most other changes simply refine many of the same features that are new to IE 7. Version 2 polishes tabbed browsing, newsfeed support, and add-on management. Regrettably, you'll still find some sites written specifically for IE that don't look right in Firefox 2. However, you can add a plug-in that will let you view a site in IE to get around the problem; my favorite is IE View (https://addons.mozilla.org/firefox/35/). You can download a near-final release candidate 3 Wednesday here: http://mozilla.com/firefox. The final version should be available at the same site within a week, and existing users of the browser will receive a notice about version 2 once Mozilla has made a minor update to version 1.5 a few weeks after version 2 is out.

Microsoft had further to go to bring IE up to par with the competition (IE 6 was released in 2001), and so IE 7 is a more thorough overhaul of its predecessor. You can't miss the new user interface, with tabbed browsing, integrated searching, and newsfeed support. Microsoft also added an antiphishing tool and boosted IE 7's security in response to seemingly never-ending IE 6 holes. Over a few months, the company will prod users to get version 7 via Automatic Updates; you can also download it from Microsoft's site at http://microsoft.com/ie. (A final version for Windows Vista will ship with Vista early in 2007.)

For this story, we evaluated feature-complete release candidates of both browsers, IE7 RC1 and Firefox 2 RC2, prior to their final release.

Tabbed upgrades

IE 7's new streamlined look resembles Vista's. The back, forward, and favorites buttons, and the address bar, are all compressed into two rows up top, along with a new search box you can customize with your choice of search engine. You won't see a menu row with standard XP options like File, Edit, or View (you can bring it back if you want). But you will see welcome new tabs -- which you can drag-&-drop to arrange as you wish -- for viewing multiple pages within one IE window.

You also get a new session-saver option: When you close the browser, you can click a box to have IE remember your open tabs, then open the same ones next time. This small but highly useful feature could gradually make a big difference in your daily browsing.

The tabs don't get their own row, however, so they can start to appear somewhat squished if you have many open at once. To navigate, you can click a small button that shows thumbnail previews of all your open tabs on a new, temporary page, and then click one of the thumbnails to activate its tab. You can also select from all open tabs via a drop-down list accessed via a small button to the left of the tabs.

While less obvious, Firefox 2's tab updates are generally a step ahead of IE's. For example, you can configure Firefox to always save your last session for future use; with IE 7 you have to click a box every time. Firefox also lets you reopen closed tabs via the History menu or by right-clicking an open tab.

As in IE's implementation, each Firefox tab has its own closing button. However, Firefox provides no thumbnail previews of open tabs.

Better news

RSS feeds offer a great way to quickly check news and updates from different sites without visiting them all. RSS support is new to IE 7, and upgraded in Firefox 2.

In IE, if you browse a page with an associated feed, an icon to the right of the tabs will light up. Click it, and you'll see the latest headlines from that feed along with an option to subscribe. Once you subscribe, you can check it via the feeds button in the new Favorites Center, where you'll also find your browsing history. However, you have no way to quickly preview the feed's contents without opening the feed's rendered page in IE, which somewhat defeats the purpose--you may as well visit the regular site. Microsoft says that it deliberately designed IE's feed support to be bare-bones because it is meant as a platform for future RSS reader applications.

Using Firefox 1.5's Live Bookmarks, you can bookmark a feed and then preview all its headlines at once. If you click a headline, you go to that story on the relevant site--but if you click a link that opens the feed itself, you see only Web-code gibberish. Firefox 2 makes the raw feed understandable, and offers a range of new subscription options. For example, you can now add a feed to a personal Bloglines, Google Reader, or My Yahoo page, or to a stand-alone RSS reader, though it may not work with all readers.

Safer browsing

Both browsers add antiphishing features meant to protect against malicious fake sites that attempt to trick users into divulging their log-ins or financial information. Firefox's default protection stops at comparing sites against a known blacklist of phishing sites, while IE 7 includes site analysis that will try to warn you about a suspicious site even if it's not yet on a blacklist, an approach similar to that implemented in the latest security suites.

According to the folks in Redmond, IE 7 will scan a page for phishing hallmarks in the URL or page content. The addresses of suspicious sites will get sent to Microsoft, where they're compared against a blacklist. If a site is on the list, IE will block the page. If it's a known good site, you'll see the page. If the site is unrecognized, you'll get a warning. Microsoft says it protects your privacy and the URL queries it receives, but it does save the data.

Testing page content (as opposed to relying solely on a blacklist) is a good idea since phishing sites typically have very short life spans, or they shift Web addresses quickly as the crooks behind them race to nail a few victims before being blacklisted.

By default, Firefox compares sites against a locally stored blacklist--meaning you won't have to send out lists of the URLs you visit -- and displays a warning if it sees a match. However, you can instead choose to send the URLs you visit to Google, which will compare them against a more frequently updated list. Google doesn't associate the information it logs with other personal data about you, but the URL or other page information sent may itself include personal data that will be logged.

IE 7's new security features go beyond an antiphishing tool. For example, its "Delete Browsing History" option clears temporary files, cookies, history, form data, and passwords, either all at once or separately, something you can already do in Firefox 1.5. You also get a new "Fix Settings for Me" feature that warns you if you reset security settings to something Microsoft deems unsafe.

Microsoft has also improved ActiveX handling, tightened the program's code, and changed the underlying architecture to reduce potential areas of attack for hackers. Overall, the new IE has many more security fixes than the revised Firefox. But such fixes were necessary to address IE 6's many holes, including some recent ones that allow drive-by downloads that can fill your PC with malware if you visit a poisoned site.

Moreover, while Firefox has its share of security flaws, Mozilla has proven much faster at patching them.

Bountiful add-ons

Firefox users have long been able to select from a vast assortment of free extensions that add functionality--ranging from improved RSS reading to security enhancements to ad blocking -- which increases that browser's appeal to many users. IE 7 is taking aim at that advantage with a new add-on manager, as well as an accompanying Web site (http://ieaddons.com) to promote and distribute the extras.

Microsoft doesn't quite hit the target, however. You can enable, disable, and delete add-ons in IE's manager, but it's not very user-friendly; for example, the manager offers no descriptions of the add-ons. Also, to see all possible extensions, you must go through four categories that themselves are far from intuitive: add-ons currently loaded in Internet Explorer, add-ons that have been used by IE, add-ons that run without requiring permission, and downloaded ActiveX controls (32-bit). Moreover, to update your plug-ins, you must manually check for new versions and download each one.

By contrast, Firefox 2 builds on a good thing with a revamped manager that controls themes and extensions in one window. As before, each one has a description, and a Find Updates button quickly checks for updates for every add-on.

It can be great fun to tinker your way to a fully customized browser with extensions, but you can risk slowing things down by using more system resources. Firefox users have griped about its memory usage in the past, and while Mozilla often blames add-ons, the company says version 2 uses significantly less memory than version 1.5 does.

Mostly smooth upgrades

When you install the new IE (a roughly 15MB download), you'll be prompted to check for updates and then run Microsoft's malicious-software removal tool, which scans for viruses. The first time you launch IE 7, you'll also see a new page asking you to choose a default search engine and whether to run the antiphishing guard.

The new IE will save your old bookmarks and some settings, including your chosen privacy level for handling cookies. Other items may be reset. In my informal test, IE 7 reset my custom security configurations for the Internet zone to the Medium High default setting; if your security is set to High, however, IE 7 will preserve it.

Microsoft also says that IE 7 won't try to change your default browser if your choice is not IE, and that it should use roughly the same system resources as version 6.

The Firefox 2 download is a much smaller 5MB, and also seems to use fewer resources than IE 7. In my informal tests immediately after installing and launching IE 7, the browser with three open tabs used 80MB of memory; under similar conditions and with the same three tabs, Firefox used 58MB. Otherwise, the performance of the two browsers appeared similar.

When you install Firefox, you'll see a pop-up prompt to check for updates to themes and extensions you have that aren't yet compatible with the new version. Popular extensions typically update quickly; other add-ons and many themes can take weeks longer. If you have incompatible add-ons, the browser upgrade will still occur, but those add-ons will be disabled in version 2 until updated extensions are available (check by clicking the Find Updates button in the add-ons manager).

Firefox preserved my bookmarks and most of my test settings from version 1.5, including my master password for saved log-ins and my chosen default font. The cookie setting didn't transfer because my particular choice (to allow sites to set cookies unless I have removed their cookies in the past) isn't the same in Firefox 2. You'll find some settings in different areas of the Options window, also; for example, password preferences are now under Security instead of Privacy.

Let the wars rage

IE 7 includes other new features, such as quick page zooms and enhanced Web page programming support. Such tweaks, combined with the browser's major improvements, might slow or even halt the generally steady IE-user flight toward Firefox.

But it's telling that the last time we compared the major browsers, back in January, we looked at beta versions of Firefox 1.5, IE 7, and Opera 9. Mozilla will effectively lap Microsoft by releasing both 1.5 and 2 in the time Microsoft took to complete IE 7. (Opera remains at version 9.)

Which one should you use? For satisfied Firefox 1.5 users, moving to version 2 is a no-brainer, as they'll get new features and won't be thrown off by major interface changes. Confirmed IE users have a similarly easy choice: IE 7's features make it a much better browser than 6.x, and its security enhancements alone make it a must-have.

Of the two rivals, Firefox remains the better application. Since IE users will have to adjust to a new layout and interface anyway, this might be a good time to give Firefox a try, then watch IE 8 play catch-up again in five years.