Is it worth switching to a new browser Marc Andreessen never had to force users to ask that question when he built Mosaic in 1993. For most early adopters, it was their first browser.

But now he's backing the development of another browser, RockMelt. This browser is not perfect, but it does show that there's room yet in the market. If Facebook built a browser, it would probably look a lot like this.

This has been tried before. The other social Web browser, Flock, integrates Facebook features. Also, like Flock (at least the new 3.0 version), RockMelt is built from Chromium, the same Google-developed open toolkit underneath the Chrome browser.

RockMelt is solid effort and is worth trying. Here are some reasons you will probably like it' and, to be fair, some things that may turn you off:

RockMelt is called the &34'Facebook browser&34' for a good reason. It gives you two dashboard wings: the left-hand wing shows you which Facebook friends are online' the right lets you drill into your social services, RSS feeds, and plug-ins.

It's a real social browser RockMelt shows which of your friends are online on Facebook, right in your browser. If you want to share something from the Web, you'll know who's going to see it right away. It makes sharing links and pages more engaging than using Twitter or even Facebook's site. (Downside: you can't scroll the left-hand "Facebar," which is sorted alphabetically, so unless you filter your friends by your RockMelt favorites, you'll always see your "A" friends on your list but you may never see your "Zs.")

Yet the social aspect is not overwhelming RockMelt puts your friends in a narrow bar on the left, and status badges for sites (Facebook and Twitter, plus RSS feeds and plug-ins) in a skinny bar along the right. On wide-screen and large monitors, these dashboards are at once informative and unobtrusive. The design works. Flock's social sidebar has the cool feature of pulling status updates from all your social networks into one stream, but it's more in your face than RockMelt's.

Sharing is fun and easy. So is updating There's a "share" button near the URL entry field. You can share pages to Facebook or Twitter easily and intuitively. The same button lets you send links as private messages directly to specific Facebook users (but not as direct messages to Twitter friends.)

If this were a Facebook browser, by the way, it'd probably say "Like" instead on the Share button. Look for that change when Facebook buys out this company.

You can also send out Facebook and Twitter status updates without sharing anything. It's equally easy and fast, although the status update button is in a different part of the browser frame.

It has a really slick search function RockMelt breaks with Chrome's single URL and search box concept and gives you an old-fashioned search field alongside, just like ye olde Firefox. When you search in the RockMelt field, you get a drop-down window with results that pre-cache into the background. As you cursor down the list, the page behind the window updates fast. Power browsers will appreciate a tiny but wonderful "add as tab" button in each result in the search window that opens a result in a new tab without changing your focus to it. Got a lot of results you want to visit later Click, click, click. They're loaded into tabs that you can get to at your leisure.

You can still search in the URL field, as with Chrome, but RockMelt's search is better.

It's fast like Chrome Although it appears to be a bit of a process hog, RockMelt is fast. There's no speed penalty for the social features.

It does RSS better than any other browser If you're on a site with an RSS feed, a little icon lights up to let you know it. It's a snap to subscribe to the feed and add a site icon into your right-hand sidebar. RSS results display in a scrolling window, with previews. The RSS preview window doesn't have the same functionality as the search results window, however.

The beta has a great invitation system During the beta period, when you go to the RockMelt site, you're asked to sign in with Facebook. If you request an invitation, your Facebook friends who are on RockMelt will see that you're awaiting access when they open up their browser. Any one of them can then hook you up. As a pal on Twitter said, "It makes the inviter and invitee feel special."

RockMelt is still beta and it feels like it. Things you might want to think about before you dive in include the security and privacy issues of hitching a Facebook app so tightly to your browsing history. Also, RockMelt is not based on the most recent or safest build of Chromium.

It also looks like some of RockMelt's cloud-based services are overwhelmed at the moment. My social sidebars wouldn't load into RockMelt on a Windows machine after a restart of the browser, and the invitation system wouldn't find all my friends when I wanted it to.

And while Chrome plug-ins will load into RockMelt, I found some that didn't display their content correctly. RockMelt also needs a few more networking services layered into it (like LinkedIn, perhaps, or Gmail). But Facebook and Twitter are good starting points.

I don't know if I'll still be using RockMelt next week, but assuming the bugs get squashed in the product and that the company can reassure users about privacy, I can't see strong reasons to avoid this browser. It's fast, it's got a really great search feature, and while it is a social browser, it's subtle about it. It's well worth taking for a spin.