Norton toolbar present in Firefox but missing from list of firefox extensions

Hi all,

I recently visited my Firefox Extensions page and found a blank page with a message saying I didn't have any extensions, despite them being there on the screen.  After visiting the Mozilla Forum and getting their advice (involving deletion of various "extensions" files and recreating them, I now have my Extensions page populated again, EXCEPT for the Norton Toolbar listing.  It's there and when I right-click in the menu area it's there and ticked.  Screen cap attached, where you can see the icons for the extensions and the Norton Toolbar.  Any ideas, please?

Ian