I use both Firefox and Thunderbird. Really cool programmes. I especially like the tabbed browsing and the included download manager. On occasion I have to use IE6, when going to the MS website or when some of the other websites dont work with Firefox.
Thunderbird is also very userfriendly. I experimented with Eudora and Incredimail and various others like Outlook and Outlook Express. Dont want to use any of those mail clients, thanks to Thunderbird!