Do you have multiple keyboard layouts installed? It is possible that you have switched the keyboard layout by accident. * http://support.microsoft.com/kb/258824 - How to change your keyboard layout Windows remembers the keyboard layout setting per application and you may have changed the keyboard layout by accident via a keyboard shortcut. * http://windows.microsoft.com/en-US/windows7/The-Language-bar-overview The Language bar (overview) * 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 You can consider to disable the key sequence to rotate the keyboard layout. * Control Panel > Regional and Language Options > Keyboards and Languages > Change keyboards > Advanced key settings > Change key sequence