Been using Firefox and Thunderbird here for the past year, nice alternatives to IE and Outlook. Especially love the tabbed browsing of Firefox.
As for Norton, there was something a while back that Norton was interfering with on my computer, something was messing with Outlook Express so I couldn't get ANY emails. I found out that it was a known issue with Norton. Since then I have canned them and use Grisoft AVG for my virus scanning.