OK, thanks.
I assume you mean 'Norton IPS 1.0' and 'Norton Toolbar 3.5' when you refer to extensions in NIS 2009 not working with Firefox 3.5? If so, you should be OK to use FF 3.5 from this coming Wednesday (15th). I've got NIS 2009 too and have just waited for the update with the 2 extensions disabled.
More info
here from the Norton Community forum.