Who changed my function keys? F7 and F8 functions have been overwritten in Windows 7
Go to your Start menu and look for the shortcut for Mozilla Firefox. Right-click it and then at the bottom of the list select Properties. You should hopefully see something like this window:
Where my Shortcut Key says CTRL + ALT + SCROLL LOCK you can click in that box and press the backspace key to delete the shortcut.
If the key is not assigned to the shortcut on the start menu you may also need to look at the desktop icons.