For years, the Web browser was a technology that seemed frozen in time. While the Web itself exploded with new types of content and virtual communities, the way users accessed that material changed hardly at all from 1997 to 2004 (not coincidentally, the years when Microsoft’s Internet Explorer had a chokehold on the browser market).

But now with a maturing base of open-source code for building Web tools, browser technology is thawing quickly – and upstart software engineers are bringing into question some long-dominant assumptions about the way browsers can and should work.

Browster, for example, offers a free add-on for Internet Explorer and the Mozilla Foundation’s open-source Firefox browser that’s a simpler alternative to using the “Back” button. The San Francisco company lets people viewing a Web page, say, a list of Google search results, see what lies beyond the hyperlinks simply by placing the mouse over those links – without having to click on them or open a new window.

Meanwhile, companies like San Francisco-based Flock are developing entirely new browsers designed from the beginning to facilitate now-common social activities, such as blogging, RSS-based news reading, and photo sharing.

The new technologies promise to help Web browsers catch up with the Web itself – which is bursting with material contributed by users themselves. “The Web today is very different from the Web of the ’90s, which was very much a one-to-many experience,” says Peter Andrews, a senior software engineer at Flock and the lead builder of Sage, an open-source extension for Firefox that speeds up the process of scanning through RSS feeds. “Now you have a growing community of producers building a many-to-many Web – and browsers should integrate the functionality to support that.”

Of course, new versions of the most popular Web browsers come along regularly. Microsoft released Internet Explorer 7 Beta 2 on April 24; Mozilla upgraded Firefox to version 1.5.0.4 on June 1. But while each release includes a few more bells and whistles – IE7 allows tabbed browsing in imitation of Firefox, for example – the basics of Web browsing haven’t really changed since the University of Illinois’s National Center for Supercomputing Applications created the first browser, Mosaic, in 1994.

Searchers move about the Web by left-clicking on hyperlinks. The browser responds to each click by opening a new page in the same window or, if the user chooses, a new tab or window. Returning to a previously viewed page – such as a list of search results – means either clicking the “back” button or switching tabs or windows.

This tried-and-true procedure works well enough, and has become so familiar that it feels preordained. But is it the best way? Is there room for change? Scott Milener thinks so. He and a friend, Wendell Brown, stumbled onto that subject while having lunch one day in 2004. “I asked Wendell, ‘Have you noticed how much we hit the back button every day?’ And he pushed me on the question. Of course the napkins started coming out, and we invented what Browster is today.”

Once a user has installed the Browster plugin, placing the mouse’s pointer over any hyperlink on a page causes a small icon to pop up. Hovering over that icon with the pointer makes a new “window” appear on top of the current page, showing the page to which the hyperlink connects.

Unlike other preview systems, such as the “binoculars” tool at Ask.com, which fetches small thumbnails of the new pages, Browster window displays the entire page at full size, just as it would appear if a user clicked to it. And moving the mouse outside the Browster window makes it disappear. In short, it spares the user the need to click back through a browsing history to recover an earlier page.

At first, Browster was intended as a way for users to quickly preview the results from search engines such as Google or Yahoo. And it’s still quickest when used that way: on search pages, the software pre-fetches the pages for every result and inserts a Browster icon next to each one, indicating that it’s been loaded into the browser’s cache. That way, the pages pop up instantly when a user mouses over the search link, explains Milener, now Browster’s CEO.

But after Milener and Brown (who is Browster’s chairman) rolled out the first version of the tool in 2005, they discovered something surprising. “Users loved the ‘hover’ icon, and they use it even more than the ‘pre-fetch’ icon on Google,” Milener says. “They’re using Browster all over the Web, just to preview pages – even though those pages are loading at the same speed they would if just clicked. In other words, the navigation function turned out to be more valuable than the pre-fetching. We realized this isn’t just a better way to preview search results – it’s really a fundamental switch in the way we navigate.”

While this change may not be completely revolutionary, it’s one of the first in a very long time. “When you look at Microsoft in the mid-90s, you have to conclude that they stifled innovation in the browser market,” says Flock’s Andrews. “They stopped Netscape in its tracks with Internet Explorer, and once they became the dominant player in browsers, they just sat on it. But now that we have the core technology that anyone can use to create a browser – the Mozilla code base, which has really come of age with Firefox – I think we’re going to see a lot of innovation.”

Flock’s developers hope to demonstrate that the Mozilla code base can be used to build a browser that’s even more versatile than Firefox, which is famous for its ability to run extensions, such as Browster’s. For example, Flock lets users upload files such as photographs to the Web by simply dragging and dropping them into the browser window. It notifies users when their friends have posted new pictures and shows the pictures directly in an area called the “photobar.” It also has a built-in feed reader, blog editor, and integrated desktop and Web search tool, as well as an enhanced “favorites” system that lets users tag and share their bookmarks.

Features like these are already available to users in the form of standalone services or Firefox plugins, but Flock’s developers believe that integrating them will provide a better user experience. “We’re building the next-generation web browser,” says Andrews. “We’re going to exceed what people are used to with Internet Explorer and Firefox right now, by integrating these services and reducing the complexity of simple tasks, say, uploading photos to Flickr or adding images to your MySpace page.”

Web users won’t have to wait long to test Flock’s theories; Andrews says a beta version will be launched “in the next few weeks.”