Make FF & Safari check boxes and buttons tabbable (tab between)

One thing I do like about IE (maybe the only thing) is how one can tab between input boxes, check boxes and action buttons. I think this makes filling out forms so much quicker and easier.

Safari and FF will tab between text input boxes, but ignore checkboxes and action buttons altogether.

Can I force Firefox and Safari to let my users tab between input boxes, check boxes and action buttons? How would I code that in?

Thanks for any help.