Similar complaints have cropped up in Norton's forums. This might help:

http://us.norton.com/support/kb/web_view.jsp?wv_type=public_web&docurl=kb20100720112959EN_EndUserProfile_en_us

Assuming that your Norton product is fully up-to-date, you might need to enable the toolbar by clicking the orange Firefox button and looking beneath the Options menu.

Thanks for that, I'm actually trying to find a solution that doesn't involve reinstalling my Norton product. Also I'm slightly confused - I'm not sure what you mean by 'the orange firefox button'. I've been through the list of extensions in the Add ons manager - hence I know that the Norton Toolbar 5.6 is compatible and enabled but I'm just not able to get it to show up on the browser and integrate with my login manager.

By click on the orange Firefox button where?