In the post, it is advise that we should not update Firefox till the compatible IPS is relases which is just a week from now. And also, mentioned in his post he commented that even if the IPS is not compatible, we are still protected. The statement can be seen here, "Yes, you are still protected. We have many layers of protection above and below the Firefox IPS plug-in. Part of the IPS technology component, SONAR and other protection engines will provide adequate support while the Firefox plug-in remains disabled." So it means that you safe.
But, should there be a new virus or whatever type of threat and that it has just been release, Norton might not be able to detect it so fast. As a result, it is best to hold off upgrading it. And Norton has also given a date for the relase of IPS. It is stated that it will be relase on the second week of February. You guys should trust Norton otherwise why are you using their product?