How to Turn Off Firefox 4 Taskbar Tab Preview

Firefox 4 starts following IE8 "All-Tab Preview" in Windows 7 taskbar. I, as a person who use browser window as "group" and tab as "document", can't get along with this paradigm. So what I should do this turn it back to old "Window Preview" mode.

about:config can always help you tweaking your Firefox, just search for "preview" and turn browser.taskbar.previews.enable to "false".