See Norton support for help with their software. Here's a thread about Firefox 5.0 /5.0.1 and the Norton Toolbar.
http://community.norton.com/t5/Norton-Internet-Security-Norton/Norton-Toolbar-for-Firefox-5/td-p/475704/page/21

I'm no computer genius, but not a total idiot, either. I've spent the better part of (2) days trying to install Norton search safe toolbar on the supposedly latest version of Firefox, and now I'm only just one step closer to seeking mental therapy !!!! I've done the best I could with forum suggestions, and even chatted with Norton directly and followed their instructions, but still no toolbar.....there has to be a better way !! Maybe Firefox should try using Internet Explorer's program that was pretty much a 'no brainer' even for me !