I've been using Firefox for a while now and there is NO reason to go back to IE. Yes, it is faster. I never get a popup and with adblock extention the ads go away too. I never have adware or spyware on my system....always clean.
Thunderbird is the no-brainer choice to go along with Firefox. It is at 1.0 now too. Only downside is Hotmail won't work but that is what Gmail is for!
My theme of choice for Firefox is Noia 2.0 lite.
Go Firefox!