Developers at the Mozilla Foundation are readying the first alpha version of the Firefox 2 open-source browser, and could release it as early as Tuesday. The release includes a new "Places" feature intended to make it easier to find and return to recently visited webpages.

The development team decided to freeze the code for what will become Firefox 2.0a1 as of last Thursday, with a view to releasing the code this Friday, according to the minutes of a Firefox 2 status meeting held March 14 at the foundation’s headquarters. However, another notice posted to the webpage of the Mozilla Developer Center advised that the Thursday code freeze could lead to a release as early as Tuesday.

The foundation’s "tinderbox" server, which automatically recompiles and packages the latest Firefox code as it is updated, listed a package labeled firefox-2.0a1 as available for download last week, prompting some Mozilla watchers to claim the alpha version had already been released.

However, that file is for internal use, and Mozilla engineers in Mountain View, Calif., will officially release the software when they have finished testing it, according to Tristan Nitot, president of Mozilla Europe.

If testing goes well then the software will be released, but if it uncovers major problems, they will be fixed and the testing process will begin again, he said.

"You can never be sure of the [release] date. It might be tonight, it might be Friday," he said.

Unlike beta versions of software, which are usually feature-complete but may contain bugs, the first alpha release of Firefox 2 will lack many of the new features planned for the final version.

One of the hallmarks of Firefox is "tabbed browsing," allowing users to flip between views of different webpages they have opened by clicking on "tabs" like those found in a card index. Firefox developers plan to add an "undo close tab" feature to help users return to a page for which they have accidentally closed the tab, but this feature has now been pushed back to the second alpha release, due next quarter, according to the minutes of the status meeting.

An on-the-fly spelling checker for text typed into Web forms was also pushed back to the alpha 2 release because of difficulties integrating the code into the foundation’s e-mail client, Thunderbird.

Features included in the alpha 1 release include the Places dialog, which makes it easier to find and return to previously visited pages based on their content rather than their address, and a system for remotely disabling third-party extensions to the browser. These extensions can be installed by users to add functionality or change the behavior of the browser, but may cause it to crash or pose a security risk. Firefox 2 will consult a list of extensions on a central server and refuse to load those that the Mozilla developers consider unsafe.