Intermittent Norton Toolbar Issue with Firefox 18

I'm using Firefox 18.0.2 and have the very latest NIS having repeatedly run live update.  I have in the Firefox extenstions:

 

Norton toolbar 2013.3.1.3 and Norton Vulnerablity Protection 11.1.1.5 - 3 and both are enabled.

 

I've been using FF18 for ages now with no issues, but now sometimes it opens with the Norton Toolbar and other times without it.  This is happening on both my laptop and my desktop ramdomly and re-starting Firefox and/or the computer does not always bring the Norton toolbar back.

 

I've looked through the forums but can't see any threads with this issue.  Has anyone else had this and found a cure?