Helen
There are two workarounds in that thread now -- go into the part of FIrefox that controls add-ons and disable all the Norton ones. Having no experience of Firefox I can't say anything more about that nor do I know what if anything of importance is inactive as a result. Since it seems to be to do with the Norton Toolbar it may be that you just lose the green flags for non-risky website sort of things.
The other, if you want to try it, is the most certain and that is to uninstall NIS 2010 (users have said using the Norton Removal Tool but don't do this if you have any other Norton applications installed since it removes everything Norton without selections, including things like GHOST and I'm not sure that it is necessary) and then reinstall NIS 2010.
If you have the installation disk you could use this and let it update because I understand that the offending update has been removed from the liveupdate servers or you can download this 81MB file and install that since it is the .136 version or should be:
New NIS 2010: Click on this link NIS 2010
Just download it using the Save option and then double click it to run it and you should be back to where you were.
Hugh | 
