I don't use Norton, so I can't check this, but I have a guess. Extension developers typically specify a range of compatible Firefox versions. Firefox often ignores this range so that older extensions continue to work on new versions of Firefox, but developers can state that the range should be strictly observed and then Firefox will disable the extension on non-matching versions.

I do not know if that toolbar has binary components.
Binary components always need to be compiled against the Gecko version, so extensions that contain such binary components won't work properly with the Firefox version other than they are specified for.