As we showed you yesterday, recent prerelease builds of Chrome 13 have an experimental new user interface option that allows users to hide the navigation bar. But Google isn't the only browser vendor trying to shed toolbar pixels. Mozilla Labs has published an add-on that brings a similarly svelte design to the Firefox Web browser.

The new add-on, which is called LessChrome HD, can be installed in Firefox 4. It will cause all of the toolbars below the tabs to automatically hide when they aren't in use. The toolbars will emerge when the user's mouse cursor moves over a tab or when an empty tab is active. It will also show up briefly when the user switches tabs. Unlike the equivalent Chrome feature, the LessChrome add-on doesn't try to reduce the horizontal space consumed by the popup toolbars.

The LessChrome HD add-on is an experiment that is intended to shed light on how this kind of interface reduction impacts usability. There is no plan yet to incorporate it into future versions of the browser, though it could hypothetically happen someday.

Much like Chrome's hidden navigation bar option, the LessChrome add-on seems well-suited for netbooks and other environments with constrained screen space. One inherent advantage of this feature in Firefox compared to Chrome is that Firefox's toolbar customization natively allows users to put whatever user interface elements they want in the tab bar. This means that the user can selectively choose the features that they want to have persistently visible even when the toolbars are hidden.

The idea behind LessChrome comes partly from an ongoing Mozilla Labs experiment called Home Dash that offers a radically unconventional HUD-style navigation and tab management interface. Home Dash goes much further than other browsers in streamlining on-screen interface elements, but the changes it brings would likely be too extreme to appeal to regular users. LessChrome HD reflects a more pragmatic and incremental approach to interface reduction.