You need to do that while Firefox has focus because Windows remembers the keyboard layout setting per application.
Check the keyboard language (keyboard layout) setting for the application that has focus via the icon on the Language bar.
You can do that via the right-click context menu of the Taskbar: Toolbars > Language Bar.
Make sure that you have the Language bar visible on the Windows Taskbar.
Windows remembers the keyboard layout setting per application and you may have changed the keyboard layout by accident via a keyboard shortcut. It is possible that you have switched the keyboard layout by accident by using the key sequence to rotate the keyboard layout.
Firefox options, preferences and settings.
Accessibility features in Firefox - Make Firefox and web content work for all users.
Wingdings font works in Firefox with Windows but not with Linux.
Keyboard doesn´t use the correct symbols.
Symbols on some keyboard number keys misrepresented on screen, namely 2,3 and 6 are " / and ?.