Seems to me you're doing something wrong..
Like what?
If Firefox is so perfectly standards compliant and the javascript worked perfectly well with FF2, then it should work perfectly well on the alledgedly perfectly compliant Firefox 3, shouldn't it?
But then, if Firefox was actually so perfect, it wuld be at Version 1.0, wouldn't it? Actually, I know the reason and it is due to one of the many bugs in Firefox.
As I've said before, Firefox is a pile of junk. So is Internet Explorer. Neither are properly standards compliant. The difference is that Microsoft's developers are arrogant and don't pay much attention to feedback, while Firefox developers are sanctimonious and don't believe any feedback about their cherished product.
Can you tell I'm not impressed by either bunch? Just don't fall into the trap of thinking either is better than the other. They are just awful in different ways.