First of all, I have used Firefox and Thunderbird exclusively since Microsoft stopped providing security updates for IE run under anything but Winblow$ XP. Not a single infestation of any spyware, adware, malware or trojan.
In all fairness to Micro$haft, I also run Norton Internet Security Firewall and Antivirus.
For spyware, I also run:
Spybot Search & Destroy (Freeware)
AdWare Away (FYJ Software)
CWS Shredder (Freeware)
Ever since I spent 12 hours (not an exaggeration) de-infesting my daughter's computer (Winblow$ XP, non-updated McAfee Antivirus) of multiple (and I do mean MULTIPLE) infestations of viruses, malware, adware, spyware and trojans, I have become more convinced that the answer lies in multiple layers of defense, not in any single product. Since I have zero confidence in anything that Micro$haft produces that "enhances" anything other than their bottom line, I feel they can keep their "free" program. I have enough of their crap to keep updated for security problems. I don't need any more.