The latest beta of Internet Explorer 7 has leaked onto the Net, revealing publicly some of the features Microsoft has been promising.

Explorer developers have also recently detailed changes to a central feature of many prominent Web-based apps, while developers at rival Firefox have previewed some of the features in version 2.0 of the open-source browser, due this summer.

Explorer 7 is expected in the next two months. Beta 2 build 5299 was released as a .rar file by Windows enthusiast site on Friday, and was apparently downloaded by tens of thousands of users before the link was removed at Microsoft's request.

The site also published a number of screenshots of the build, displaying features such as tabbed browsing. Tabs, like many of the other features coming in Explorer 7, have been supported in competing browsers for months, if not years. supplied a patch allowing the build to be installed on pirate copies of Windows XP, and as of Tuesday afternoon said it had been downloaded more than 18,000 times.

Explorer 7 changes
On a more official front, developers on the IE Blog revealed that the XMLHTTP ActiveX control will be exposed as a native script object in the upcoming browser. The change has implications for so-called "Web 2.0" applications using what are known as AJAX features.

XMLHTTP, allowing XML data to be sent via the HTTP protocol, is central to AJAX, which allows Web applications to behave more like desktop applications. One of the first tools to popularise AJAX was Google's Gmail.

In current versions of Explorer, XMLHTTP is available only as an ActiveX object. That means when administrators switch off ActiveX, for security or other reasons, AJAX-based sites won't work.

"In Explorer 7, XMLHTTP is now also exposed as a native script object," wrote Sunava Dutta, a programme manager on the Explorer team. "Users and organisations that choose to disable ActiveX controls can still use XMLHTTP-based Web applications." Explorer 7 will continue to support the XMLHTTP ActiveX control as well.

Dutta said the implementation will be consistent with that of other browsers, simplifying cross-browser compatibility.

Last week, it was revealed that Explorer 7 will allow users to delete their browsing history in one step, something long offered by other browsers.

Firefox 2.0
While Explorer trumpets its introduction of tabs, Ben Goodger, lead engineer for Mozilla Firefox, has said Firefox 2.0 will take tabbed browsing to the next level, making tabs behave more like windows on the desktop.

Goodger detailed the changes on his official Mozilla blog.

Other plans for the upcoming browser include changes to the bookmark and history systems, improving the user interfaces for discovery and handling of RSS and Atom type feeds, making the search interface more discoverable and adaptable, and freshening the overall visual design.

Goodger said major improvements may be on the way for those who increasingly rely on the text input area of the browser for using Web-based mail, blogs and other content management systems. "The rise of applications like web mail, blogging, etc. highlight the weaknesses of HTML's textarea widget," he wrote. "We should at the very least offer people the ability to spell check their submissions."

He said Firefox 2.0 is planned for mid-2006, with conservative planning hopefully getting around some of the delays that dogged version 1.5. "The idea of Firefox 2 is to deliver significant user experience enhancements on top of a relatively stable rendering engine," he wrote. "Significant retooling (will be) done on the main development trunk for what will become Firefox 3."

He said Firefox 2.0 is based on the same branch of the Gecko rendering engine used for version 1.5. "They should be compatible from a Web developer's point of view. APIs might be added, but none should be changed."