IE vs. everything else
Everyone not using IE (icky poo) needs to know how it wants to intrude at every opportunity before using Firefox, Opera, Mozilla et al. The whole Windows won't work without IE thing.
I'm pretty handy with PCs (helped setup Texaco's PC help desk in the early 80's) and moved directly to Mozilla then FireFox when I upgraded to XP, and worked backwards. If Yahoo's mail client functioned fully w/ Firefox, I'd have no need to every run IE.
As Firefox gets more and more popular, the cracker community will start writing malware for it. Based on past experience, it's reasonalbe to expect that Mozilla will be more forthright than MicroHard... opps, I mean MicroSoft with problems and patches.