FireFox is a browser
Windows is an operating system
I understand how silly headlines can confuse people.
Get FireFox at http://www.mozilla.org/products/firefox/
FireFox is currently less vulnerable because it does less (that is pretty much how the model works - expanded functionality means expanded vulnerability and less options means less vulnerability - this is not rocket science). Home users - by all means switch to FireFox.
Yeah, I know, my mistake. But Windows and IE are almost synonymous.
IE doesn't have tabbed browsing (great) or pop-up blockers (even greater.)
I don't think that's quite what's in play here... IE, because of it's integration with the OS, has built-in vulnerabilities. Firefox doesn't share those limitations. The only thing I haven't been able to do is browse some sites written specifically for IE, which has more to do with lazy, non-standard website authoring than it does IE.
Firefox is loaded with features that IE doesn't have. Firefox also doesn't use system-level libraries as its engine and therefore any compromise of Firefox isn't automatically a system-level compromise.