User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:2.0) Gecko/20100101 Firefox/4.0 Build Identifier: Mozilla/5.0 (Windows NT 6.1; rv:2.0) Gecko/20100101 Firefox/4.0 In a certain situation, the Firefox window size is lost when maximising the window. Reproducible: Always Steps to Reproduce: 1. Place the Firefox window in the middle of the screen, not maximised 2. Restart Firefox -> Window position is remembered 3. Maximise the window using Aero Snap (drag the window against the top edge of the screen) 4. Restart Firefox -> Window is maximised again 5. Restore the Firefox window using Aero Snap (drag the window away from the top edge) -> Restored position is remembered 6. Maximise the window again Now it's getting harder :-) 7a. Restore the window with Aero Snap, but keep the mouse button pressed 7b. While the mouse button is still pressed, maximise the window again by pushing it against the top egde 8. Restart Firefox 9. Now restore the window again Actual Results: Now the window has the size of the entire screen. The restored position is not correctly remembered. Expected Results: The window should be as small as it was set before starting the experiment. The bug always seems to happen when the window is restored and maximised in one step using Aero Snap and then Firefox is restarted in maximised state. Could it oversee a window state change notification?

Similar? https://bugzilla.mozilla.org/show_bug.cgi?id=665249

Looks like bug 581697 to me, which was fixed in Firefox 8. I can't reproduce this with Firefox 12 beta.