The venerable dialog box, long a staple of software design, faces extinction or at least endangered-species status in Firefox.
Mozilla designer Stephen Horlander has published Firefox interface mock-ups that illustrate how the browser could look with some options set through a preferences tab rather than through a preferences dialog box.
The designs are experimental, but some of the work is proceeding already. For example, Firefox's new interface for managing add-ons uses this "in-content" interface, and Firefox's about:config controls have appeared in a browser tab for years.
Moving away from dialog boxes is by no means universal, but it is common. Dialog boxes can be confusing, sometimes blocking access to the rest of the software until they're closed and sometimes staying open while hidden behind other windows. Some software, such as Photoshop, is moving toward "non-modal" controls that often live alongside content in the manner of a toolbar.
The Firefox in-content approach is one of many interface changes under way as Mozilla works to release Firefox 4. Among other changes are hardware-accelerated graphics and text; "app tabs" that load Web applications in all browser windows; support for multitouch interfaces; and the new Firefox theme that among other things puts the list of tabs along the top of the browser rather than underneath the address bar.