User-Agent: Mozilla/5.0 (Windows NT 5.2; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0 Build Identifier: When toggling into fullscreen, the taskbar is temporarily drawn on top of the window. When browser.fullscreen.animateUp is set (the default), the taskbar is drawn over the window until the animation begins, which looks sloppy. When that preference is unset, it's worse: it can take several seconds before the window appears over the taskbar. If the ^F Find box is open at the bottom of the window, the window never appears over the taskbar at all until the browser window loses and regains focus. This makes entering fullscreen much less seamless than it should be. Chrome's behavior here is worth modelling: pressing F11 toggles to fullscreen instantly, with no delays. Tested in XP and XP64. This only happens when fullscreening a maximized window. Reproducible: Always