I use Safari and Firefox, but I rarely have both of them running at the same time. I would like to press a function key (say, F1) and have the system switch to whichever browser happens to be running and bring it to the front. Is this possible, perhaps with AppleScript? I currently have F1 assigned to Safari and F2 to Firefox (via DragThing), and it works as long as I remember which browser is running. But too often I press the wrong function key and then the other browser launches, which is not what I want.