I'm sure this is an easy one but I'm not finding anything on Google. Instead of typing a number, the one and two keys on my keyboard send me either backwards or forwards a tab in Firefox. This has happened for the past few days and I think I've probably activated a shortcut accidentally. For some reason it happens when typing in some text boxes and not in others (e.g. I can type the numbers fine in title boxes, as above, but not in body text boxes like this one).
Any ideas how to shut it off?