Firefox 2.0 has been released by the Mozilla Foundation, just a few days after the latest release of competing browser Internet Explorer.

New features in the open-source Firefox software include a spell checker for Web forms, anti-phishing warnings, and improved search and tabbed browsing capabilities.

Most Firefox 1.5 extensions will work with the 2.0 browser, but add-on maintainers will need to make some slight changes to let the Firefox 2.0 browser know that their software is compatible. "If you've got an add-on that somebody wrote three years ago that they're no longer maintaining, then that's maybe a bit more problematic," said Mike Beltzner, a user interface expert with the open-source project.

The 2.0 browser has been criticised for its lack of major new features, but it does include a very large number of smaller bells and whistles, as well as many bug fixes, according to Beltzner. "This is a very different product from Firefox 1 or 1.5," he said.

Downloads of the software had been "incredibly smooth" and the company expect a "large bulk" of Firefox users to shift to the new version within the next month. Those users expecting their browser to automatically install version 2.0 may have to wait a little longer. Firefox's automatic update feature does not presently give users the option of declining an update. And because some users may not want to move to version 2.0, Firefox will first ship a 1.5.0.8 upgrade to the browser that will give them the ability to decline the major upgrade. After that it will push out the 2.0 version via automatic update.

This 1.5.0.8 release will also include some bug fixes, Beltzner said. It is expected to be delivered by the end of next month, he added.