Business sector of the Internet market is IE, hands down. Can't touch it.
As for downloads, you can control what IE does in the background. Besides, most of the hidden access-hacks are through the ActiveX controllers, which is not IE's fault, and is a downside to the power of ActiveX. If you turn off ActiveX, you'll find IE a lot more secure.
Although it's just a moot point if you're intelligent about your security. Use a firewall and AV, keep them up to date like you're supposed to, and you're fine.
As for Firefox...*sigh*...look, it's a neat and nice little browser alternative and a great place to send the MS bashers...but it ain't up to snuff yet.
I mean, try running a FLASH movie with the transparency parameter on. You'll see bug number one.
Then of course there's the whole layers issue. Layers in IE, guaranteed to be the same every load. Layers in Firefox...I feel like I'm shooting craps with a three sided dice.
With IE, I can take today's latest technologies, and the technologies of the past, write them into my pages, load them, and I know they're going to run and run the way I see them in my WYSIWYG. I can't say the same for Netscape, Firefox, Opera, etc. etc. After I get done making a page, I load it in IE, okay, happy, then go load it in Netscape/Firefox/Opera, sigh, and start working on workarounds to deal with the limitations of those browsers.
It's freaking annoying.
Plus if I want to do any Intranet/web-app work, it's gonna be IE hands-down anyway, so why bother?
Protect yourself.
Be smart.
Keep it simple.
Stop wasting my time.