Mozilla will use a several-week delay it recently added to the Firefox 3.1 schedule to build a private browsing mode and beef up the browser's address bar, the company said yesterday. Three weeks ago, the company said it would insert four to five more weeks into the timetable, part of a reaction to changes in the browser market, including the introduction by Google of its Chrome browser. Then, Mozilla said it would probably use the time to add a privacy mode and to punch up its TraceMonkey JavaScript engine performance.

A private browsing mode and fast JavaScript execution were touted by Google last month when it launched Chrome.

In meeting notes published on its Web site today, Mozilla said it planned to add the privacy feature in Beta 2, which would likely be released in November according to Mozilla's current schedule.

Dubbed "porn mode" by some, privacy tools limit or entirely eliminate what the browser records as it travels the Internet. Typically, URLs are not recorded in the history, cookies are not saved and other evidence is purged from the computer at the end of the session. Microsoft's Internet Explorer 8, Chrome, and Apple's Safari all have private browsing built in.

Also set for debut in Firefox 3.1 Beta 2: changes to the already-available "Clear Private Data" tool that would let users select time and data ranges for retroactively erasing their browsing tracks, changes to the address bar to add privacy-related tagging and tab search, and a restoration of the plug-in installation process used in Firefox 2.0.

Already slated to appear in Beta 1, Mozilla said today, were support for the video HTML tag, tab bar tweaks, and the ability to drag a tab to the desktop to open a new browsing window.

Mozilla is also mulling over several other additions to Firefox 3.1, but has not committed to working them into the release. The most prominent would be an Opera-esque "Speed Dial" feature that would show user-selected or most-recent sites as thumbnails when the user opened a new tab. Google's Chrome sports a similar tool.

The developer who has taken charge of the proposed Firefox feature cited a pair of existing add-ons, Speed Dial and Fast Dial , as examples of what he was considering.

Mozilla made it clear, however, that those last-wave changes would not have priority. "We're also considering reviewed, solid, tested patches for some other small improvements but we will not hold Beta 2 for these," the meeting notes said.

Beta 1 is on track for release next week, while Beta 2 will be locked down November 4 and released several weeks after that, Mozilla said. It has not committed to a ship date for Firefox 3.1, but has said it will shoot for a late-2008 or early-2009 release.