But just how good is Chrome? How does it differ from IE and from less popular, but still important, browsers like Mozilla’s Firefox and Apple’s Safari?

I’ve been testing Chrome for about a week, trying out all its features and using it side by side with Microsoft’s latest iteration of IE, which came out just last week.

My verdict: Chrome is a smart, innovative browser that, in many common scenarios, will make using the Web faster, easier and less frustrating. But this first version — which is just a beta, or test, release — is rough around the edges and lacks some common browser features Google plans to add later. These omissions include a way to manage bookmarks, a command for emailing links and pages directly from the browser, and even a progress bar to show how much of a Web page has loaded.

Chrome’s interface has some bold changes from the standard browser design. These new features enhance the Web experience, but they will require some adjustment on the part of users. For instance, Chrome does away with most menus and toolbar icons to give maximum screen space for the Web pages themselves. Also, Google has merged the address bar, where you type in Web addresses, with the search box, where you type in search terms. This unified feature is called the Omnibox.

One striking difference in Chrome is how it handles tabs, which display a single Web page. In Chrome, each tab behaves as a separate browser. The bookmarks bar, Omnibox, menus and toolbar icons are located inside the tab, rather than atop the entire browser. The tabs appear at the top of the computer screen. Chrome also groups related tabs. If you open a new tab from a link in a page that’s already open, that new tab appears next to the originating page, rather than at the end of the row of tabs.

Despite Google’s claims that Chrome is fast, it was notably slower in my tests at the common task of launching Web pages than either Firefox or Safari. However, it proved faster than the latest version of IE — also a beta version — called IE8.

Meanwhile, Microsoft hasn’t been sitting still. The second beta version of IE8 is the best edition of Internet Explorer in years. It is packed with new features of its own, some of which are similar to those in Chrome, and some of which, in my view, top Chrome’s features.

Google’s Chrome browser displays thumbnails of a user’s most-visited pages when a new tab is opened, rather than a blank page.

For example, while IE8 also groups related tabs, it assigns a different color to each such tab group and allows you to close them all with one click. It has a “smart” address box of its own, that drops down a list of suggestions as you type, though it retains a separate search box.

IE8 also has breakthrough privacy features that exceed Chrome’s, and includes a new technology called Accelerators, which allows you to take rapid action on any selected word or phrase on a Web page, such as generating a map for a place name, without switching to a new page.

As they develop, each of these browsers has a good chance of besting Firefox 3.0, which I have regarded as the best Web browser for Windows, the only operating system on which Chrome currently runs. But they will have to get faster at loading pages. And, to best Firefox on the Macintosh, Google will have to make good on its promise to produce a Mac version of Chrome, something it says it will do in the coming months. Microsoft has no plans to produce a Mac version of IE8.

Chrome and IE8 are far more advanced than Apple’s Safari. Safari is speedy on both Mac and Windows platforms, but lacks many of the key intelligent features of its newer Google and Microsoft rivals.

Why is Google igniting a new browser war? There are two main reasons, and both involve competing with Microsoft. First, the search giant fears that because its search engine and other major products depend on the browser, Microsoft — with its rival online products — might be able to gain an advantage by altering the design of IE, which has roughly a 75% market share.

Second, and more important, Google sees the Web as a platform for the software programs, or applications, that currently run directly on computer operating systems, notably Microsoft’s Windows. It says current browsers lack the underlying architecture to enable future, more powerful Web applications that will rely more heavily on a common Web programming language called JavaScript. Chrome was designed to be the world’s speediest browser at handling JavaScript.

That move might one day make Chrome a sort of online operating system that competes with Windows. “Think of Chrome as more than a simple Web browser,” Google declares. “It’s a platform for running Web applications.”

Microsoft’s IE8 has an “Accelerator” feature that lets users select any Web text and then map, translate, search or email their selection without leaving the page.

I tested Chrome, and IE8, on a plain-vanilla Lenovo ThinkPad laptop running Windows XP, and equipped with a modest processor and one gigabyte of memory.

To gauge Chrome’s speed at loading Web pages, I launched two large groups of typical Web pages simultaneously, each site opening in its own tab. One group included 15 sports sites, the second 19 news sites. In both tests, Chrome’s speed fell in the middle, at 35 and 44 seconds, respectively. IE8 was slower, taking 49 and 75 seconds to open the two groups of sites. But Firefox and Safari were much faster, notching identical speeds of 19 seconds for the 15 sites and 28 seconds for the 19 sites.

Google claims that future, more sophisticated Web applications relying more heavily on JavaScript than today’s sites do would run faster on Chrome. Of course, I couldn’t test any claim about future scenarios, but I did run Chrome on several JavaScript test sites, used by developers. It handily beat the other browsers. However, Google doesn’t claim users would see much difference on current Web application sites.

I also tested Chrome’s compatibility with scores of common Web sites. In general, it did well, rendering the sites properly. But I ran into problems with video. Some video sites refused to recognize Chrome, because its development has been a secret. On others, like Major League Baseball’s site, videos mostly played properly, but sometimes didn’t.

IE8 also has some compatibility issues, for different reasons. It’s the first version of Internet Explorer to hew closely to Web standards. Earlier versions used some nonstandard ways of rendering Web sites, prompting some site designers to adopt techniques that made their pages work in IE, but look odd in Firefox and Safari. Now, ironically, these pages also look strange in IE8. So Microsoft was forced to build in a special Compatibility View button that users must click to see the sites properly.

Chrome is built on three core design principles. The first is its spare user interface: just two menus and a handful of toolbar icons. IE introduced a similar approach in its version 7, but with a difference. Microsoft allows users to restore a traditional menu bar; Google doesn’t. The only toolbar icon you can add in Chrome is a Home button.

The second principle is that a user can type anything into a single place, the Omnibox, and instantly get suggestions on where to go, gleaned from the user’s own browsing history and Google’s rankings of popular sites. Whether you type in a Web address or a search term, the Omnibox is very smart. In my tests, it sometimes came up with the right destination after I typed only one or two letters of the name of a site I often visited.

The Omnibox has another cool feature: Tab-to-Search. If you type in the name of another site that includes its own search feature, like Amazon.com, the Omnibox lets you just press the tab key to search within that site, without opening it first. Chrome, through its Options settings, also lets you change the default search engine used by the Omnibox. Instead of Google’s own search service, you can use Microsoft’s Live search, Yahoo search, or others.

The third big principle behind Chrome is that each tab runs, under the hood, as a separate browser. Tabs can be dragged off the main browser and turned into separate windows. If one tab crashes, the rest of the browser keeps running. But this doesn’t work perfectly. In my tests, all of Chrome died on me when I tried watching an Olympics video on the NBC site.

You can even make a tab a standalone application that runs from the Start Menu, or the desktop, as if it was a separate program.

Chrome has a few other key features. When you open a new tab, you don’t get a blank page, but a set of thumbnails for your most-visited pages, plus lists of recent search engines you’ve used, recently used bookmarks and recently closed tabs.

Like other browsers, Chrome puts up a warning when you try to visit a malicious or phony Web site, and it has a private browsing mode, called Incognito, which allows you to browse without leaving any history on your computer — a feature popularized in Safari.

Chrome also has a pop-up blocker, but it’s annoying because it flashes a notice that a pop-up has been blocked. IE also does this, but unlike in Chrome, the warnings are much less intrusive.

Internet Explorer 8 has some new features Chrome lacks. Its private browsing mode, called InPrivate, is the first I’ve seen that not only leaves no traces on your own computer, but also bars Web sites from collecting some types of information on where you’ve previously been surfing.

While IE8’s address box and search box remain separate, each also offers rapid suggestions; and both are organized better than Chrome’s. For instance, the suggestions that drop down from its address bar are divided neatly into categories drawn from the browser’s own guess, your history and your favorites. One downside: For this to work in Windows XP, you must first install Microsoft’s desktop search product.

Like Chrome, IE8 lets you switch your default search provider, but it also allows you to switch search engines on the fly. When you type in a search term, icons for alternate search engines appear at the bottom of the suggestion list, and you need only click on these to see search results from, say, Google, instead of Microsoft’s own Live search engine.

IE8’s Accelerators feature presents a blue-arrow icon above any text on a Web page that you have selected. Clicking on the icon brings up a list of actions you can take using the selected text, such as posting it to a blog, emailing it, mapping it or searching it. While these actions are set by default to use Microsoft’s own Web services, you can change them to use Google’s, Yahoo’s, or those from other companies.

Microsoft also has built in a feature called Web Slices. These are portions of a Web site that a site developer can designate to appear in the IE8 Favorites bar and to constantly update themselves. An example might be bidding on eBay.

Like Chrome, IE8 also displays useful information whenever you create a new tab, including a list of recently closed tabs and a list of Accelerators.

With the emergence of Chrome, consumers have a new and innovative browser choice, and with IE8, the new browser war is sure to be a worthy contest.

Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com. Email him at mossberg@wsj.com.

Trying to share information with people on your Web-based networks can introduce another layer of digital jujitsu. It can be awkward to snag a photo or a snippet of text from one Web site and send it to a friend in a social network on another, or post it to your own blog.

But I’ve been testing a little-known Web browser that attempts to solve these problems. It’s called Flock, and it bills itself as “the social Web browser.” I found that it worked well, but it isn’t for everyone, and it has some important downsides.

Flock is a modified version of the excellent Firefox Web browser that tacks on some special features for social networkers and bloggers. It’s available free at flock.com in essentially identical versions for Windows, Mac and Linux.

Flock adds a special vertical “sidebar” at the left of the browser that keeps your social networks, photo sites or news feeds visible at all times, regardless of what page you’re viewing in the main browser window.

For instance, with Flock, you can see that you have a new friend request in Facebook, or that a pal has posted new photos in Flickr, without clicking away from reading this column in the main browser window.

But, wait: There’s more. With one click, you can display a horizontal “media bar” across the top of the browser containing thumbnails of all of a friend’s photos or videos from a social-networking or photo site, again without changing what’s in the main browser window.

These two special bars also allow you to take action. For instance, you can just drag images and text from Web pages into the sidebar to share them with friends listed there. And any photo on the media bar can be quickly emailed or posted to a blog.

There’s also a “Web clipboard,” which can save any text, image or link from a site in the main window by merely dragging it to the Flock sidebar. Once an item is in this clipboard, it stays there until you delete it.

Flock has its own built-in blog editor, which allows you to quickly compose, edit and publish blog posts containing interesting items you encounter on the Web. And it creates a special personal Web page, called My World, which combines your social-networking updates, news feeds and photos.

I found Flock productive and fun to use. I tested its special sidebar with my Facebook, Flickr, Picasa and YouTube accounts, and with my favorite news feeds. I also used another of Flock’s features, which let me check my Gmail and Yahoo Web-mail accounts without navigating to their main pages. And I published several posts from within Flock to a test blog I maintain. All of this worked as promised.

In my tests, I used the latest edition of Flock, version 2.0, which is built on the new Firefox 3.0 browser. Even though this latest iteration of Flock is still in beta status, I found it to be quite stable.

But Flock isn’t for everyone, and it has some significant drawbacks. For one thing, you’d need a fairly large or high-resolution monitor to accommodate the Flock sidebar and media bar without reducing the size of the main browser window so much as to require too much scrolling. Even with a big or high-res screen, you will see fewer toolbar links and browser tabs than normally.

And, Flock has a busy, even frenetic, look that can be distracting and annoying. So many things are going on at once that it can be hard to concentrate on the main attraction: the Web page you are reading in the main window.

Also, while Flock does indeed spare you from clicking back and forth as often among tabs in your browser, it doesn’t entirely eliminate clicking around. Its sidebar can display only one type of information at a time — social networks and photo-sharing sites in one view, news feeds in a second, the clipboard in a third, and Web bookmarks in a fourth. So you’ll have to click the sidebar’s own controls fairly often to check all of these, or keep going to the special My World page in the main window.

Finally, Flock works with only certain social networking, photo-sharing and blogging services. While it does support most of the main ones, there are some glaring omissions. MySpace isn’t yet on the list, though it’s expected to be added next month. But Hotmail, Windows Live Spaces and SmugMug, among others, are missing. And it doesn’t support any instant-messaging services at all.

Flock does a good job at the tasks it sets for itself, but I would recommend it for only the heaviest and most impatient social networkers. For most others, Flock is overkill.

Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com. Email him at mossberg@wsj.com.