Firefox

Firefox in my opinion is superior to Explorer at this point with Firefox’s extensions. I use Fasterfox, NoScript, SafeCache, SafeHistory, AdBlock, and IE Tabs.

Adblock – Prevents advertisements from displaying on webpages. This is my favorite extension.
No Script prevents webpages from using Java or Javascript unless you grant permission
Fasterfox prefetches webpages which makes things load in background while you surf.x
IE Tabs if you have a page that only works in Explorer (ie active X) you can permanently open it up in a explorer tab within firefox. I use this for hotmail and windows updates.

Safe History, Safe Cache – I know they were developed by much more computer saavy programmers than myself so I’ll take the claim that it increases firefox security.

I use the Blue Ice Theme.