See: * http://windows.microsoft.com/en-US/windows7/The-Language-bar-overview The Language bar (overview) It is possible that you are switching the keyboard layout by accident. * Make sure that you have the Language bar visible on the Windows Taskbar. * You can do that via the right-click context menu of the Taskbar: Toolbars > Language Bar. * Check the keyboard language (keyboard layout) setting for the application that has focus via the icon on the Language bar. * You need to do that while Firefox has focus because Windows remembers the keyboard layout setting per application. * The default to rotate the layout is a key combination (Ctrl+Shift or Alt+Shift) that you can easily use in Firefox to activate a menu item. * Disable the key sequence to rotate layouts (Alt+Shift or Ctr+Shift) to avoid an unintentional switch and instead assign a specific key (Alt/Ctrl+Shift+number) to switch to the keyboard layout. * Vista/Windows 7: Control Panel > Regional and Language Options > Keyboards and Languages > Change keyboards > Advanced key settings > Change key sequence