It is possible that you accidentally switched the keyboard layout. 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. See: http://support.microsoft.com/kb/306993 - HOW TO: Use the Language Bar in Windows XP http://windows.microsoft.com/en-US/windows-vista/The-Language-bar-overview - The Language bar (overview) .... 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. Windows remembers the keyboard layout setting per application. The default to switch 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. For XP see: Control Panel > Regional and Language Options > Languages > Text services and input languages > Details > Key Settings > Change Key Sequence For Vista see: Control Panel > Regional and Language Options > Keyboards and Languages > Change keyboards > Advanced key settings > Change key sequence ..... http://support.microsoft.com/kb/258824 - How to change your keyboard layout