User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b13pre) Gecko/20110303 Firefox/4.0b13pre Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b13pre) Gecko/20110303 Firefox/4.0b13pre When maximized, FF4 extends the tabs to almost touch the screen edge; the clickable region extends to the screen edge. This is great (Fitts law) and makes it easy to just sweep up the mouse and hit a tab. However, there are a few pixels between tabs near the top of the tab bar that aren't claimed by any tab and are thus respond to clicks the way the title bar would. Due to these tiny regions of title-bar pixels, clicks can go astray and cause surprising behavior. In particular, when dragging a tab (which you'll commonly end up doing on the top row of pixels due to Fitts law) and missing, the window is unmaximized and dragged instead. More annoying, when closing multiple tabs in succession using middle-mouse-button clicks, if, due to a mis-click or due to the tabs resizing and the boundary region thus moving, you middle-mouse button click on the title bar, the firefox window will be sent to the back - i.e. disappear - without any obvious cause. Reproducible: Always Steps to Reproduce: 1. Open a maximized notepad window (or any other application. 2. Open a maximized firefox window with several tabs and put it in front. 3. Middle click on the top-row of pixels - try to hit the pixel(s) between two tabs. Actual Results: If you hit a tab, that tab closes, but if you happen to hit one of the two or three pixels between tabs on that top pixel row, firefox's window is sent to the back (e.g, behind notepad in this example) Expected Results: When clicking between two tabs on the top pixel row, firefox should treat that as a click on one of the two tabs, just as it would a few rows down.