Windows 7. Firefox 28.0. Hardware acceleration is off in both profiles. Default profile behaves normally in the primary monitor (I have two monitors). When I open the default in the secondary monitor, it appears to be at maximize size but only the top bar of the screen is visible. If I shrink it, it locks up, but I can slide it over to the primary monitor where it then works normally. If I open it in the primary monitor then move it to the secondary, it shows in a less than full screen. When I maximize it, a duplicate screen partially opens and both freeze, and menus freeze when I open them. I can slide it back to the primary where it works normally. My other profile is an old one with all the bookmarks, settings and history. It works fine on both monitors.