Clean up casuing loss of settings

Hi all,

A simple one (I hope) and it may not even be a Norton issue.  I regularly lose my settings, eg Gmail log in list on Firefox, eg earlier today, I had four possible Gmail addresses to choose from.  When I woke the PC up this evening, they'd all gone and I had the annoying text message verification check to perform.  Is there a Norton setting I've missed that keeps deleting my settings?

Thanks,

Ian